chore: add constraints file check for python samples (#80)

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Source-Link: googleapis/synthtool@0a071b3

packages/google-cloud-billing-budgets/.github/header-checker-lint.yml

@@ -1,6 +1,6 @@
 {"allowedCopyrightHolders": ["Google LLC"],
  "allowedLicenses": ["Apache-2.0", "MIT", "BSD-3"],
- "ignoreFiles": ["**/requirements.txt", "**/requirements-test.txt"],
+ "ignoreFiles": ["**/requirements.txt", "**/requirements-test.txt", "**/__init__.py", "samples/**/constraints.txt", "samples/**/constraints-test.txt"],
  "sourceFileExtensions": [
  	"ts", 
  	"js", 

packages/google-cloud-billing-budgets/renovate.json

@@ -2,5 +2,8 @@
   "extends": [
     "config:base",  ":preserveSemverRanges"
   ],
-  "ignorePaths": [".pre-commit-config.yaml"]
+  "ignorePaths": [".pre-commit-config.yaml"],
+  "pip_requirements": {
+    "fileMatch": ["requirements-test.txt", "samples/[\\S/]*constraints.txt", "samples/[\\S/]*constraints-test.txt"]
+  }
 }

packages/google-cloud-billing-budgets/synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/python-billingbudgets.git",
-        "sha": "794cf739e8cb93b8143b0cfcc9fd2f7d070e6256"
+        "sha": "4e18234f1815c3f2bc210f8215bc621e9916d20e"
       }
     },
     {
@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "5b5bf6d519b2d658d9f2e483d9f6f3d0ba8ee6bc"
+        "sha": "0a071b3460344886297a304253bf924aa68ddb7e"
       }
     }
   ],