Bump mnemosyne-ruby from 1.12.1 to 1.13.0

Bumps [mnemosyne-ruby](https://github.com/jgraichen/mnemosyne-ruby) from 1.12.1 to 1.13.0.
- [Release notes](https://github.com/jgraichen/mnemosyne-ruby/releases)
- [Changelog](https://github.com/mnemosyne-mon/mnemosyne-ruby/blob/main/CHANGELOG.md)
- [Commits](https://github.com/jgraichen/mnemosyne-ruby/compare/v1.12.1...v1.13.0)

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

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

Gemfile.lock

@@ -244,7 +244,7 @@ GEM
       path_expander (~> 1.0)
     minitest-server (1.0.6)
       minitest (~> 5.0)
-    mnemosyne-ruby (1.12.1)
+    mnemosyne-ruby (1.13.0)
       activesupport (>= 4)
       bunny
     msgpack (1.5.1)