fix: don't allow -self-hosted mode as container image (#1783)

* fix: don't allow `-self-hosted` mode as container image

* fix: jobcontainer in hostmode platform

* Update run_context.go

---------

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: ChristopherHX

pkg/runner/run_context.go

@@ -420,8 +420,9 @@ func (rc *RunContext) startContainer() common.Executor {
 }
 
 func (rc *RunContext) IsHostEnv(ctx context.Context) bool {
-	image := rc.platformImage(ctx)
-	return strings.EqualFold(image, "-self-hosted")
+	platform := rc.runsOnImage(ctx)
+	image := rc.containerImage(ctx)
+	return image == "" && strings.EqualFold(platform, "-self-hosted")
 }
 
 func (rc *RunContext) stopContainer() common.Executor {
@@ -474,14 +475,20 @@ func (rc *RunContext) Executor() common.Executor {
 	}
 }
 
-func (rc *RunContext) platformImage(ctx context.Context) string {
+func (rc *RunContext) containerImage(ctx context.Context) string {
 	job := rc.Run.Job()
 
 	c := job.Container()
 	if c != nil {
 		return rc.ExprEval.Interpolate(ctx, c.Image)
 	}
 
+	return ""
+}
+
+func (rc *RunContext) runsOnImage(ctx context.Context) string {
+	job := rc.Run.Job()
+
 	if job.RunsOn() == nil {
 		common.Logger(ctx).Errorf("'runs-on' key not defined in %s", rc.String())
 	}
@@ -497,6 +504,14 @@ func (rc *RunContext) platformImage(ctx context.Context) string {
 	return ""
 }
 
+func (rc *RunContext) platformImage(ctx context.Context) string {
+	if containerImage := rc.containerImage(ctx); containerImage != "" {
+		return containerImage
+	}
+
+	return rc.runsOnImage(ctx)
+}
+
 func (rc *RunContext) options(ctx context.Context) string {
 	job := rc.Run.Job()
 	c := job.Container()