fix(spanner): update the API

#### spanner:v1

The following keys were changed:
- schemas.RequestOptions.properties.requestTag.description
- schemas.RequestOptions.properties.transactionTag.description

discovery/spanner-v1.json

@@ -1923,7 +1923,7 @@
       }
     }
   },
-  "revision": "20210325",
+  "revision": "20210405",
   "rootUrl": "https://spanner.googleapis.com/",
   "schemas": {
     "Backup": {
@@ -3376,11 +3376,11 @@
           "type": "string"
         },
         "requestTag": {
-          "description": "A per-request tag which can be applied to queries or reads, used for statistics collection. Both request_tag and transaction_tag can be specified for a read or query that belongs to a transaction. This field is ignored for requests where it's not applicable (e.g. CommitRequest). `request_tag` must be a valid identifier of the form: `a-zA-Z` between 2 and 64 characters in length",
+          "description": "A per-request tag which can be applied to queries or reads, used for statistics collection. Both request_tag and transaction_tag can be specified for a read or query that belongs to a transaction. This field is ignored for requests where it's not applicable (e.g. CommitRequest). Legal characters for `request_tag` values are all printable characters (ASCII 32 - 126) and the length of a request_tag is limited to 50 characters. Values that exceed this limit are truncated.",
           "type": "string"
         },
         "transactionTag": {
-          "description": "A tag used for statistics collection about this transaction. Both request_tag and transaction_tag can be specified for a read or query that belongs to a transaction. The value of transaction_tag should be the same for all requests belonging to the same transaction. If this request doesn’t belong to any transaction, transaction_tag will be ignored. `transaction_tag` must be a valid identifier of the format: `a-zA-Z{0,49}`",
+          "description": "A tag used for statistics collection about this transaction. Both request_tag and transaction_tag can be specified for a read or query that belongs to a transaction. The value of transaction_tag should be the same for all requests belonging to the same transaction. If this request doesn’t belong to any transaction, transaction_tag will be ignored. Legal characters for `transaction_tag` values are all printable characters (ASCII 32 - 126) and the length of a transaction_tag is limited to 50 characters. Values that exceed this limit are truncated.",
           "type": "string"
         }
       },

src/apis/spanner/v1.ts

@@ -1176,11 +1176,11 @@ export namespace spanner_v1 {
      */
     priority?: string | null;
     /**
-     * A per-request tag which can be applied to queries or reads, used for statistics collection. Both request_tag and transaction_tag can be specified for a read or query that belongs to a transaction. This field is ignored for requests where it's not applicable (e.g. CommitRequest). `request_tag` must be a valid identifier of the form: `a-zA-Z` between 2 and 64 characters in length
+     * A per-request tag which can be applied to queries or reads, used for statistics collection. Both request_tag and transaction_tag can be specified for a read or query that belongs to a transaction. This field is ignored for requests where it's not applicable (e.g. CommitRequest). Legal characters for `request_tag` values are all printable characters (ASCII 32 - 126) and the length of a request_tag is limited to 50 characters. Values that exceed this limit are truncated.
      */
     requestTag?: string | null;
     /**
-     * A tag used for statistics collection about this transaction. Both request_tag and transaction_tag can be specified for a read or query that belongs to a transaction. The value of transaction_tag should be the same for all requests belonging to the same transaction. If this request doesn’t belong to any transaction, transaction_tag will be ignored. `transaction_tag` must be a valid identifier of the format: `a-zA-Z{0,49\}`
+     * A tag used for statistics collection about this transaction. Both request_tag and transaction_tag can be specified for a read or query that belongs to a transaction. The value of transaction_tag should be the same for all requests belonging to the same transaction. If this request doesn’t belong to any transaction, transaction_tag will be ignored. Legal characters for `transaction_tag` values are all printable characters (ASCII 32 - 126) and the length of a transaction_tag is limited to 50 characters. Values that exceed this limit are truncated.
      */
     transactionTag?: string | null;
   }