Bump rdoc from 6.6.0 to 6.6.3.1 in /test_app

Bumps [rdoc](https://github.com/ruby/rdoc) from 6.6.0 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@v6.6.0...v6.6.3.1)

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

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

test_app/Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: ..
   specs:
-    administrate-field-active_storage (0.4.1)
+    administrate-field-active_storage (1.0.1)
       administrate (>= 0.2.2)
       rails (>= 7.0)
 
@@ -178,7 +178,7 @@ GEM
       racc (~> 1.4)
     nokogiri (1.15.5-x86_64-linux)
       racc (~> 1.4)
-    psych (5.1.1.1)
+    psych (5.1.2)
       stringio
     public_suffix (4.0.6)
     puma (5.6.4)
@@ -224,7 +224,7 @@ GEM
       thor (~> 1.0, >= 1.2.2)
       zeitwerk (~> 2.6)
     rake (13.1.0)
-    rdoc (6.6.0)
+    rdoc (6.6.3.1)
       psych (>= 4.0.0)
     regexp_parser (2.2.0)
     reline (0.4.0)
@@ -257,7 +257,7 @@ GEM
       activesupport (>= 5.2)
       sprockets (>= 3.0.0)
     sqlite3 (1.4.2)
-    stringio (3.0.9)
+    stringio (3.1.0)
     thor (1.3.0)
     tilt (2.0.10)
     timeout (0.4.1)