fix: docker proxy probe for podman and containerized runners (#1231)

Podman creates a missing bind source instead of rejecting it, so the Docker proxy probe passed even when the daemon could not see the runner's files. Jobs of Podman runners in a container got an empty directory at `/var/run/docker.sock` (https://gitea.com/gitea/runner/issues/1193#issuecomment-1700501).

The probe now binds the directory and stats its marker through the created container. A runner in a container stats the marker through its own container, so it no longer creates probe containers, which cost up to 2s per job. `make test-dind TARGET=podman` runs the probe against Podman in CI.

Reviewed-on: https://gitea.com/gitea/runner/pulls/1231
Reviewed-by: bircni <[email protected]>
Co-authored-by: silverwind <[email protected]>

.gitea/workflows/test.yml

@@ -53,6 +53,8 @@ jobs:
       # after `make test` so the images it needs are already present on the host daemon.
       - name: test against dind image
         run: make test-dind
+      - name: test against podman
+        run: make test-dind TARGET=podman
       - name: coverage report
         run: |
           make coverage-report