Skip RBS tests for RDocPluginParserTest caused by interface change of RDoc 6.14.0

https://github.com/ruby/ruby/actions/runs/15199473008/job/42750815986?pr=13421

```
 Error: ArgumentError: wrong number of arguments (given 0, expected 1)
  /Users/runner/work/ruby/ruby/src/lib/rdoc/store.rb:123:in 'initialize'
  /Users/runner/work/ruby/ruby/src/gems/src/rbs/test/rbs/rdoc/rbs_parser_test.rb:8:in 'Class#new'
  /Users/runner/work/ruby/ruby/src/gems/src/rbs/test/rbs/rdoc/rbs_parser_test.rb:8:in 'RDocPluginParserTest#parser'
  /Users/runner/work/ruby/ruby/src/gems/src/rbs/test/rbs/rdoc/rbs_parser_test.rb:147:in 'RDocPluginParserTest#test_instance_method_comment_and_tokens'
```

Author: hsbt

tool/rbs_skip_tests

@@ -37,6 +37,9 @@ TestInstanceNetHTTPResponse depending on external resources
 
 test_TOPDIR(RbConfigSingletonTest) `TOPDIR` is `nil` during CI while RBS type is declared as `String`
 
+# Incompatibility changes with RDoc 6.14.0
+RDocPluginParserTest
+
 ## Unknown failures
 
 # NoMethodError: undefined method 'inspect' for an instance of RBS::UnitTest::Convertibles::ToInt
@@ -45,4 +48,3 @@ test_linear_time?(RegexpSingletonTest)
 test_new(RegexpSingletonTest)
 
 ## Failed tests caused by unreleased version of Ruby
-