Bump net-imap from 0.4.14 to 0.4.15

Bumps [net-imap](https://github.com/ruby/net-imap) from 0.4.14 to 0.4.15.
- [Release notes](https://github.com/ruby/net-imap/releases)
- [Commits](ruby/net-imap@v0.4.14...v0.4.15)

---
updated-dependencies:
- dependency-name: net-imap
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -289,7 +289,7 @@ GEM
     mutex_m (0.2.0)
     net-http (0.4.1)
       uri
-    net-imap (0.4.14)
+    net-imap (0.4.15)
       date
       net-protocol
     net-pop (0.1.2)