ci: sync with netresearch/.github templates/go-app (#550)

Auto-opened by sync-template.sh. Brings this repo back into alignment
with the canonical `go-app` template in `netresearch/.github`.

To keep any diverging files, add their paths to
`.github/template.yaml`'s `intentional-drift:` list before merging —
otherwise the next sync run will revert them.

Author: CybotTM

.github/dependabot.yml

@@ -36,3 +36,6 @@ updates:
       interval: weekly
       day: monday
     open-pull-requests-limit: 2
+    groups:
+      devcontainers:
+        patterns: ['*']