Fix/upload artifact error windows (#27802)

From issue https://github.com/go-gitea/gitea/issues/27314

When act_runner in `host` mode on Windows. `upload_artifact@v3` actions
use `path.join` to generate `itemPath` params when uploading artifact
chunk. `itemPath` is encoded as `${artifact_name}\${artifact_path}`.

<del>It's twice query escaped from ${artifact_name}/${artifact_path}
that joined by Windows slash \.</del>

**So we need convert Windows slash to linux**.

In https://github.com/go-gitea/gitea/issues/27314, runner shows logs
from `upload_artifact@v3` like with `%255C`:

```
[artifact-cases/test-artifact-cases]   | ::error::Unexpected response. Unable to upload chunk to http://192.168.31.230:3000/api/actions_pipeline/_apis/pipelines/workflows/6/artifacts/34d628a422db9367c869d3fb36be81f5/upload?itemPath=more-files%255Css.json
```

But in gitea server at the same time, But shows `%5C`

```
2023/10/27 19:29:51 ...eb/routing/logger.go:102:func1() [I] router: completed PUT /api/actions_pipeline/_apis/pipelines/workflows/6/artifacts/34d628a422db9367c869d3fb36be81f5/upload?itemPath=more-files%5Css.json for 192.168.31.230:55340, 400 Bad Request in 17.6ms @ <autogenerated>:1(actions.artifactRoutes.uploadArtifact-fm)
```

I found `%255C` is escaped by
`https://github.com/actions/upload-artifact/blob/main/dist/index.js#L2329`.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/api/actions/artifacts_utils.go

@@ -58,7 +58,8 @@ func validateArtifactHash(ctx *ArtifactContext, artifactName string) bool {
 func parseArtifactItemPath(ctx *ArtifactContext) (string, string, bool) {
 	// itemPath is generated from upload-artifact action
 	// it's formatted as {artifact_name}/{artfict_path_in_runner}
-	itemPath := util.PathJoinRel(ctx.Req.URL.Query().Get("itemPath"))
+	// act_runner in host mode on Windows, itemPath is joined by Windows slash '\'
+	itemPath := util.PathJoinRelX(ctx.Req.URL.Query().Get("itemPath"))
 	artifactName := strings.Split(itemPath, "/")[0]
 	artifactPath := strings.TrimPrefix(itemPath, artifactName+"/")
 	if !validateArtifactHash(ctx, artifactName) {