Bump rdoc from 6.8.1 to 6.9.0 (#1840)

Bumps [rdoc](https://github.com/ruby/rdoc) from 6.8.1 to 6.9.0.
- [Release notes](https://github.com/ruby/rdoc/releases)
- [Changelog](https://github.com/ruby/rdoc/blob/master/History.rdoc)
- [Commits](ruby/rdoc@v6.8.1...v6.9.0)

---
updated-dependencies:
- dependency-name: rdoc
  dependency-type: indirect
  update-type: version-update:semver-minor
...

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

Gemfile.lock

@@ -242,7 +242,7 @@ GEM
       zeitwerk (~> 2.6)
     rainbow (3.1.1)
     rake (13.2.1)
-    rdoc (6.8.1)
+    rdoc (6.9.0)
       psych (>= 4.0.0)
     regexp_parser (2.9.3)
     reline (0.5.12)
@@ -474,7 +474,7 @@ CHECKSUMS
   railties (8.0.0.1) sha256=64261d06f39115f49e378160e4ef98903fbf14b14944a764d45e5fe2600186c6
   rainbow (3.1.1) sha256=039491aa3a89f42efa1d6dec2fc4e62ede96eb6acd95e52f1ad581182b79bc6a
   rake (13.2.1) sha256=46cb38dae65d7d74b6020a4ac9d48afed8eb8149c040eccf0523bec91907059d
-  rdoc (6.8.1) sha256=0128002d1bfc4892bdd780940841e4ca41275f63781fd832d11bc8ba4461462c
+  rdoc (6.9.0) sha256=91a9d213ac66a3c2d8c7f4e8b38eafde0ae3dd2a96c9f9f6a2620644ea54b209
   regexp_parser (2.9.3) sha256=4b620657ed8349d82e1331a076415c79b9dd714a5546162ddd790ea9988f6379
   reline (0.5.12) sha256=41ab36d3fd2aaa169e99f8b82a93b9585f51130529360e24388fcccc20a055a2
   rexml (3.3.9) sha256=d71875b85299f341edf47d44df0212e7658cbdf35aeb69cefdb63f57af3137c9