Make wiki default branch name changable (#29603)

Fix #29000
Fix #28685
Fix #18568

Related: #27497

And by the way fix #24036, add a Cancel button there (one line)

modules/git/repo_base_nogogit.go

@@ -9,10 +9,10 @@ package git
 import (
 	"bufio"
 	"context"
-	"errors"
 	"path/filepath"
 
 	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/util"
 )
 
 func init() {
@@ -54,7 +54,7 @@ func OpenRepository(ctx context.Context, repoPath string) (*Repository, error) {
 	if err != nil {
 		return nil, err
 	} else if !isDir(repoPath) {
-		return nil, errors.New("no such file or directory")
+		return nil, util.NewNotExistErrorf("no such file or directory")
 	}
 
 	// Now because of some insanity with git cat-file not immediately failing if not run in a valid git directory we need to run git rev-parse first!