samples: add presubmit lint check (#394)

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Synth log will be available here:
https://source.cloud.google.com/results/invocations/04a3c534-5129-4a05-922f-148232720a95/targets

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Source-Link: googleapis/synthtool@9602086
Source-Link: googleapis/synthtool@c3caf07

.github/workflows/samples.yaml

@@ -0,0 +1,14 @@
+on:
+  pull_request:
+name: samples
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-java@v1
+        with:
+          java-version: 8
+      - name: Run checkstyle
+        run: mvn -P lint --quiet --batch-mode checkstyle:check
+        working-directory: samples/snippets

CONTRIBUTING.md

@@ -48,11 +48,7 @@ integration tests.
 
 ```bash
 export GOOGLE_APPLICATION_CREDENTIALS=/path/to/service/account.json
-mvn \
-  -Penable-integration-tests \
-  -Dspanner.testenv.instance=projects/<your-project>/instances/<your-instance> \
-  -Dspanner.gce.config.project_id=<your-project> \
-  clean verify
+mvn -Penable-integration-tests clean verify
 ```
 
 ## Code Samples

README.md

@@ -17,7 +17,7 @@ If you are using Maven with [BOM][libraries-bom], add this to your pom.xml file
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>libraries-bom</artifactId>
-      <version>9.0.0</version>
+      <version>9.1.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>
@@ -47,11 +47,11 @@ If you are using Maven without BOM, add this to your dependencies:
 
 If you are using Gradle, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-spanner:1.60.0'
+compile 'com.google.cloud:google-cloud-spanner:1.59.0'
 ```
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-spanner" % "1.60.0"
+libraryDependencies += "com.google.cloud" % "google-cloud-spanner" % "1.59.0"
 ```
 [//]: # ({x-version-update-end})
 

synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-spanner.git",
-        "sha": "a9f90ad20698fbabca6248d3f530e44f7c2ef86b"
+        "sha": "3c78e90746d8cbc53a9d770a88b04719b1d1b90a"
       }
     },
     {
@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "f8823dec98277a9516f2fb6fae9f58b3a59a23e1"
+        "sha": "9602086c6c5b05db77950c7f7495a2a3868f3537"
       }
     }
   ],
@@ -61,6 +61,7 @@
     ".github/release-please.yml",
     ".github/trusted-contribution.yml",
     ".github/workflows/ci.yaml",
+    ".github/workflows/samples.yaml",
     ".kokoro/build.bat",
     ".kokoro/build.sh",
     ".kokoro/coerce_logs.sh",