chore: update templates (#104)

* changes without context

        autosynth cannot find the source of changes triggered by earlier changes in this
        repository, or by version upgrades to tools such as linters.

* chore: add 3.9 to noxfile template

Since the python-docs-samples noxfile-template doesn't sync with this, I wanted to make sure the noxfile template matched the most recent change [here](https://github.com/GoogleCloudPlatform/python-docs-samples/pull/4968/files)

cc @tmatsuo

Source-Author: Leah E. Cole <6719667+leahecole@users.noreply.github.com>
Source-Date: Fri Jan 15 17:24:05 2021 -0800
Source-Repo: googleapis/synthtool
Source-Sha: 56ddc68f36b32341e9f22c2c59b4ce6aa3ba635f
Source-Link: googleapis/synthtool@56ddc68

* build(python): make `NOX_SESSION` optional

I added this accidentally in #889. `NOX_SESSION` should be passed down if it is set but not marked required.

Source-Author: Bu Sun Kim <8822365+busunkim96@users.noreply.github.com>
Source-Date: Tue Jan 19 09:38:04 2021 -0700
Source-Repo: googleapis/synthtool
Source-Sha: ba960d730416fe05c50547e975ce79fcee52c671
Source-Link: googleapis/synthtool@ba960d7

* chore: Add header checker config to python library synth

Now that we have it working in [python-docs-samples](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/.github/header-checker-lint.yml) we should consider adding it to the 🐍 libraries :)

Source-Author: Leah E. Cole <6719667+leahecole@users.noreply.github.com>
Source-Date: Mon Jan 25 13:24:08 2021 -0800
Source-Repo: googleapis/synthtool
Source-Sha: 573f7655311b553a937f9123bee17bf78497db95
Source-Link: googleapis/synthtool@573f765

* chore: add noxfile parameters for extra dependencies

Also, add tests for some noxfile parameters for assurance that the
template generates valid Python.

Co-authored-by: Jeffrey Rennie <rennie@google.com>

Source-Author: Tim Swast <swast@google.com>
Source-Date: Tue Jan 26 12:26:57 2021 -0600
Source-Repo: googleapis/synthtool
Source-Sha: 778d8beae28d6d87eb01fdc839a4b4d966ed2ebe
Source-Link: googleapis/synthtool@778d8be

* build: migrate to flakybot

Source-Author: Justin Beckwith <justin.beckwith@gmail.com>
Source-Date: Thu Jan 28 22:22:38 2021 -0800
Source-Repo: googleapis/synthtool
Source-Sha: d1bb9173100f62c0cfc8f3138b62241e7f47ca6a
Source-Link: googleapis/synthtool@d1bb917

.github/header-checker-lint.yml

@@ -0,0 +1,15 @@
+{"allowedCopyrightHolders": ["Google LLC"],
+ "allowedLicenses": ["Apache-2.0", "MIT", "BSD-3"],
+ "ignoreFiles": ["**/requirements.txt", "**/requirements-test.txt"],
+ "sourceFileExtensions": [
+ 	"ts", 
+ 	"js", 
+ 	"java", 
+ 	"sh", 
+ 	"Dockerfile", 
+ 	"yaml", 
+ 	"py",
+ 	"html",
+ 	"txt"
+ ]
+}

noxfile.py

@@ -86,6 +86,7 @@ def default(session):
     session.install(
         "mock", "pytest", "pytest-cov",
     )
+
     session.install("-e", ".")
 
     # Run py.test against the unit tests.

samples/snippets/noxfile.py

@@ -85,7 +85,7 @@ def get_pytest_env_vars() -> Dict[str, str]:
 
 # DO NOT EDIT - automatically generated.
 # All versions used to tested samples.
-ALL_VERSIONS = ["2.7", "3.6", "3.7", "3.8"]
+ALL_VERSIONS = ["2.7", "3.6", "3.7", "3.8", "3.9"]
 
 # Any default versions that should be ignored.
 IGNORED_VERSIONS = TEST_CONFIG['ignored_versions']

synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/python-bigquery-datatransfer.git",
-        "sha": "5c8d7c1e860d1c50d892bfabc7ec936aaa40e714"
+        "sha": "af63f9e5605efbbf62e7e5cc12cbb02155ec262a"
       }
     },
     {
@@ -19,14 +19,14 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "16ec872dd898d7de6e1822badfac32484b5d9031"
+        "sha": "d1bb9173100f62c0cfc8f3138b62241e7f47ca6a"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "16ec872dd898d7de6e1822badfac32484b5d9031"
+        "sha": "d1bb9173100f62c0cfc8f3138b62241e7f47ca6a"
       }
     }
   ],
@@ -48,6 +48,7 @@
     ".github/ISSUE_TEMPLATE/feature_request.md",
     ".github/ISSUE_TEMPLATE/support_request.md",
     ".github/PULL_REQUEST_TEMPLATE.md",
+    ".github/header-checker-lint.yml",
     ".github/release-please.yml",
     ".github/snippet-bot.yml",
     ".gitignore",