Fix a build error

RuboCop RSpec 3.5 requires RuboCop 1.72.1+:

```console
Because rubocop-rspec >= 3.5.0 depends on rubocop >= 1.72.1, < 2.A
and rubocop >= 1.72.1, < 2.A could not be found in source at
`/home/runner/work/rubocop-ast/rubocop`,
rubocop-rspec >= 3.5.0 cannot be used.
So, because Gemfile depends on rubocop-rspec ~> 3.5.0,
version solving has failed.
```

Author: koic

.github/workflows/rubocop.yml

@@ -93,7 +93,7 @@ jobs:
         parser_engine: [parser_whitequark]
         include:
           # as well as very old specs & ancient ruby version
-          - { rubocop: "v1.61.0", parser_engine: parser_whitequark, ruby: "2.7" }
+          - { rubocop: "v1.72.1", parser_engine: parser_whitequark, ruby: "2.7" }
           # also test against the prism parser translator
           - { rubocop: "master", parser_engine: parser_prism, ruby: "3.4" }
     env: