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 <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>

act/runner/run_context.go

@@ -18,7 +18,6 @@ import (
 	maps0 "maps"
 	"net"
 	"os"
-	"path"
 	"path/filepath"
 	"regexp"
 	"runtime"
@@ -995,12 +994,8 @@ func (rc *RunContext) captureJobContainerInfo() common.Executor {
 		if rc.dockerProxy != nil {
 			rc.dockerProxy.SetMounts(info.Mounts)
 		}
-		workspace := rc.githubWorkspace()
-		for dir := workspace; dir != "/" && dir != "."; dir = path.Dir(dir) {
-			if source := info.Mounts[dir]; source != "" {
-				rc.Env["GITEA_DOCKER_WORKSPACE"] = path.Join(source, strings.TrimPrefix(workspace, dir))
-				break
-			}
+		if source := info.DaemonPath(rc.githubWorkspace()); source != "" {
+			rc.Env["GITEA_DOCKER_WORKSPACE"] = source
 		}
 		return nil
 	}