Tolerate .git directory when checking if dir is empty

Many users will be running version control; we should ignore .git
directories also therefore.

pkg/plugins/golang/v3/init.go

@@ -17,7 +17,6 @@ limitations under the License.
 package v3
 
 import (
-	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -187,8 +186,13 @@ func checkDir() error {
 			if err != nil {
 				return err
 			}
+			// Allow the whole .git directory tree
+			if info.Name() == ".git" {
+				return filepath.SkipDir
+			}
+			// Allow go.mod and dot-files
 			if info.Name() != "go.mod" && !strings.HasPrefix(info.Name(), ".") {
-				return errors.New("only the go.mod and files with the prefix \"(.)\" are allowed before the init")
+				return fmt.Errorf("target directory is not empty: only go.mod, files with the prefix \".\" and .git directories can exist before init (found %q)", path)
 			}
 			return nil
 		})