Bump rdoc from 6.5.0 to 6.6.3.1

Bumps [rdoc](https://github.com/ruby/rdoc) from 6.5.0 to 6.6.3.1.
- [Release notes](https://github.com/ruby/rdoc/releases)
- [Changelog](https://github.com/ruby/rdoc/blob/master/History.rdoc)
- [Commits](ruby/rdoc@v6.5.0...v6.6.3.1)

---
updated-dependencies:
- dependency-name: rdoc
  dependency-type: indirect
...

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

Gemfile.lock

@@ -66,7 +66,7 @@ GEM
       mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
     pg (1.5.4)
-    psych (5.1.1.1)
+    psych (5.1.2)
       stringio
     racc (1.7.3)
     rack (3.0.8)
@@ -93,7 +93,7 @@ GEM
       thor (~> 1.0, >= 1.2.2)
       zeitwerk (~> 2.6)
     rake (13.1.0)
-    rdoc (6.5.0)
+    rdoc (6.6.3.1)
       psych (>= 4.0.0)
     reline (0.3.9)
       io-console (~> 0.5)
@@ -126,7 +126,7 @@ GEM
     simplecov_json_formatter (0.1.4)
     sqlite3 (1.6.7)
       mini_portile2 (~> 2.8.0)
-    stringio (3.0.8)
+    stringio (3.1.0)
     thor (1.3.0)
     timeout (0.4.0)
     tzinfo (2.0.6)