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

@@ -252,7 +252,7 @@ GEM
       ast (~> 2.4.1)
       racc
     pg (1.5.4)
-    psych (5.1.0)
+    psych (5.1.2)
       stringio
     public_suffix (5.0.3)
     puma (6.4.2)
@@ -310,7 +310,7 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rdoc (6.5.0)
+    rdoc (6.6.3.1)
       psych (>= 4.0.0)
     recursive-open-struct (1.1.3)
     redcarpet (3.5.1)
@@ -408,7 +408,7 @@ GEM
       rubocop-performance (~> 1.19.0)
     standardrb (1.0.1)
       standard
-    stringio (3.0.8)
+    stringio (3.1.0)
     terser (1.1.18)
       execjs (>= 0.3.0, < 3)
     thor (1.2.2)