Bump rbs from 3.7.0 to 3.8.0 in /gemfiles/3.1

Bumps [rbs](https://github.com/ruby/rbs) from 3.7.0 to 3.8.0.
- [Release notes](https://github.com/ruby/rbs/releases)
- [Changelog](https://github.com/ruby/rbs/blob/master/CHANGELOG.md)
- [Commits](ruby/rbs@v3.7.0...v3.8.0)

---
updated-dependencies:
- dependency-name: rbs
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

gemfiles/3.1/Gemfile.lock

@@ -22,7 +22,7 @@ GEM
     rake (13.2.1)
     rake-compiler (1.2.8)
       rake
-    rbs (3.7.0)
+    rbs (3.8.0)
       logger
     ruby_memcheck (3.0.0)
       nokogiri