fix(deps): update dependency @google-cloud/spanner to v7 (GoogleCloudPlatform#3516)

Author: renovate-bot

functions/spanner/package.json

@@ -16,7 +16,7 @@
  },
  "dependencies": {
  "@google-cloud/functions-framework": "^3.2.0",
- "@google-cloud/spanner": "^6.0.0"
+ "@google-cloud/spanner": "^7.0.0"
  },
  "devDependencies": {
  "c8": "^8.0.0",