Update dependency @google-cloud/spanner to v2

Author: renovate[bot]

functions/spanner/package.json

@@ -17,7 +17,7 @@
     "test": "ava -T 20s --verbose test/*.test.js"
   },
   "dependencies": {
-    "@google-cloud/spanner": "1.5.0"
+    "@google-cloud/spanner": "2.2.1"
   },
   "devDependencies": {
     "@google-cloud/nodejs-repo-tools": "^3.0.0",