chore(python): use BUILD_SPECIFIC_GCLOUD_PROJECT for samples

https://github.com/googleapis/python-talent/blob/ef045e8eb348db36d7a2a611e6f26b11530d273b/samples/snippets/noxfile_config.py#L27-L32

`BUILD_SPECIFIC_GCLOUD_PROJECT` is an alternate project used for sample tests that do poorly with concurrent runs on the same project.

Source-Author: Bu Sun Kim <8822365+busunkim96@users.noreply.github.com>
Source-Date: Wed Sep 30 13:06:03 2020 -0600
Source-Repo: googleapis/synthtool
Source-Sha: 9b0da5204ab90bcc36f8cd4e5689eff1a54cc3e4
Source-Link: googleapis/synthtool@9b0da52

.kokoro/samples/python3.6/common.cfg

@@ -13,6 +13,12 @@ env_vars: {
     value: "py-3.6"
 }
 
+# Declare build specific Cloud project.
+env_vars: {
+    key: "BUILD_SPECIFIC_GCLOUD_PROJECT"
+    value: "python-docs-samples-tests-py36"
+}
+
 env_vars: {
     key: "TRAMPOLINE_BUILD_FILE"
     value: "github/python-datastore/.kokoro/test-samples.sh"

.kokoro/samples/python3.7/common.cfg

@@ -13,6 +13,12 @@ env_vars: {
     value: "py-3.7"
 }
 
+# Declare build specific Cloud project.
+env_vars: {
+    key: "BUILD_SPECIFIC_GCLOUD_PROJECT"
+    value: "python-docs-samples-tests-py37"
+}
+
 env_vars: {
     key: "TRAMPOLINE_BUILD_FILE"
     value: "github/python-datastore/.kokoro/test-samples.sh"

.kokoro/samples/python3.8/common.cfg

@@ -13,6 +13,12 @@ env_vars: {
     value: "py-3.8"
 }
 
+# Declare build specific Cloud project.
+env_vars: {
+    key: "BUILD_SPECIFIC_GCLOUD_PROJECT"
+    value: "python-docs-samples-tests-py38"
+}
+
 env_vars: {
     key: "TRAMPOLINE_BUILD_FILE"
     value: "github/python-datastore/.kokoro/test-samples.sh"

synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/python-datastore.git",
-        "sha": "8aa3eac28e0e733b61d6ab9e1d233a99467b7081"
+        "sha": "b0b778d2f27e9962f0c5f16261e2d7606c91b43c"
       }
     },
     {
@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "f3c04883d6c43261ff13db1f52d03a283be06871"
+        "sha": "9b0da5204ab90bcc36f8cd4e5689eff1a54cc3e4"
       }
     }
   ],