fix: change librarian volume to read-write in build command (#1772)

Fixes #1771

Author: JoeWang1127

internal/docker/docker.go

@@ -205,7 +205,7 @@ func (c *Docker) Build(ctx context.Context, request *BuildRequest) error {
 
 	librarianDir := filepath.Join(request.RepoDir, config.LibrarianDir)
 	mounts := []string{
-		fmt.Sprintf("%s:/librarian:ro", librarianDir), // readonly volume
+		fmt.Sprintf("%s:/librarian", librarianDir),
 		fmt.Sprintf("%s:/repo", request.RepoDir),
 	}
 	commandArgs := []string{

internal/docker/docker_test.go

@@ -197,7 +197,7 @@ func TestDockerRun(t *testing.T) {
 			},
 			want: []string{
 				"run", "--rm",
-				"-v", fmt.Sprintf("%s/.librarian:/librarian:ro", repoDir),
+				"-v", fmt.Sprintf("%s/.librarian:/librarian", repoDir),
 				"-v", fmt.Sprintf("%s:/repo", repoDir),
 				testImage,
 				string(CommandBuild),