build(deps): bump net-imap in /appengine/rails-cloudsql-mysql (#1557)

Bumps [net-imap](https://github.com/ruby/net-imap) from 0.3.8 to 0.3.9.
- [Release notes](https://github.com/ruby/net-imap/releases)
- [Commits](ruby/net-imap@v0.3.8...v0.3.9)

---
updated-dependencies:
- dependency-name: net-imap
  dependency-version: 0.3.9
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

appengine/rails-cloudsql-mysql/Gemfile.lock

@@ -208,7 +208,7 @@ GEM
     multi_json (1.15.0)
     mutex_m (0.2.0)
     mysql2 (0.5.5)
-    net-imap (0.3.8)
+    net-imap (0.3.9)
       date
       net-protocol
     net-pop (0.1.2)