chore(deps): update actions/setup-go action to v6

Author: renovate-bot

.github/workflows/conformance-tests-bigtable-proxy.yaml

@@ -46,7 +46,7 @@ jobs:
           ref: v0.0.3
           path: cloud-bigtable-clients-test
 
-      - uses: actions/setup-go@v5
+      - uses: actions/setup-go@v6
         with:
           go-version: '>=1.20.2'