Remove unnecassary calls to filepath.Join (#17608)

- Partialy resolvess #17596
- Resolves `badCall` errors from go-critic `badCall: suspicious Join on
1 argument`
- When only 1 argument is passed into `filepath.Join`, it won't do
anything special other than `filepath.Clean(...)` will be applied over
it.

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: 6543 <6543@obermui.de>

modules/repository/adopt.go

@@ -154,7 +154,7 @@ func ListUnadoptedRepositories(query string, opts *db.ListOptions) ([]string, in
 	count := 0
 
 	// We're going to iterate by pagesize.
-	root := filepath.Join(setting.RepoRootPath)
+	root := filepath.Clean(setting.RepoRootPath)
 	if err := filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
 		if err != nil {
 			return err