ci: pin runner-image v2 (adds gcc for cgo, fixes go test -race)

v1 lacked gcc, so 'go test -race' (in Makefile) failed in CI with
'go: -race requires cgo'. v2 of the runner image installs gcc,
libc6-dev, and pkg-config.

.gitea/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     # Bespoke runner image (Ubuntu 24.04 + make + git + node + go via
     # actions/setup-go). See git.librete.ch/libretech/runner-image.
     container:
-      image: git.librete.ch/libretech/runner-image:v1
+      image: git.librete.ch/libretech/runner-image:v2
     timeout-minutes: 5
     steps:
       - name: Checkout

.gitea/workflows/deploy.yml

@@ -34,7 +34,7 @@ jobs:
     # + perl + ssh, runner user pre-joined to docker gid 998 so the
     # auto-mounted /var/run/docker.sock is writable without --user root.
     container:
-      image: git.librete.ch/libretech/runner-image:v1
+      image: git.librete.ch/libretech/runner-image:v2
     timeout-minutes: 20
     if: ${{ vars.DEPLOY_ENABLED == 'true' }}
     steps: