Fetch tags with test-bundled-gems

  make test-bundled-gems failed when default branch didn't have tag ref at target repository.

  ```
  updating rbs ...
  From ssh://github.com/ruby/rbs
   - [deleted]           (none)                             -> origin/dependabot/bundler/steep/rbs-3.4.0
  remote: Enumerating objects: 68, done.
  remote: Counting objects: 100% (68/68), done.
  remote: Compressing objects: 100% (43/43), done.
  remote: Total 68 (delta 19), reused 61 (delta 18), pack-reused 0
  Unpacking objects: 100% (68/68), 204.84 KiB | 633.00 KiB/s, done.
   * [new branch]        aaa-3.4.x                          -> origin/aaa-3.4.x
   * [new branch]        dependabot/bundler/steep/rbs-3.4.1 -> origin/dependabot/bundler/steep/rbs-3.4.1
     01371463..fea0932b  master                             -> origin/master
  checking out v3.4.1 (v=3.4.1, r=) ...
  fatal: invalid reference: v3.4.1
  fatal: invalid reference: 3.4.1
  make: *** [uncommon.mk:1553: yes-test-bundled-gems-fetch] Error 1
  ```

tool/fetch-bundled_gems.rb

@@ -15,7 +15,7 @@
 
 if File.directory?(n)
   puts "updating #{n} ..."
-  system("git", "fetch", chdir: n) or abort
+  system("git", "fetch", "--all", chdir: n) or abort
 else
   puts "retrieving #{n} ..."
   system(*%W"git clone #{u} #{n}") or abort