Fixup GitHub Actions formatter when run in non-default directory

In some cases (specifically when running inside the container with
non-default `working-directory`) GitHub cannot link absolute paths
produced by formatter to the code, while relative paths works.

Output relative paths if they're inside current directory, so this
usecase is covered.

changelog/fix_github_actions_in_non_default_directory.md

@@ -0,0 +1 @@
+* [#9933](https://github.com/rubocop/rubocop/pull/9933): Fix GitHub Actions formatter when running in non-default directory. ([@ojab][])

lib/rubocop/formatter/git_hub_actions_formatter.rb

@@ -33,7 +33,7 @@ def report_offense(file, offense)
         output.printf(
           "\n::%<severity>s file=%<file>s,line=%<line>d,col=%<column>d::%<message>s\n",
           severity: github_severity(offense),
-          file: file,
+          file: PathUtil.smart_path(file),
           line: offense.line,
           column: offense.real_column,
           message: github_escape(offense.message)

spec/rubocop/formatter/git_hub_actions_formatter_spec.rb

@@ -30,6 +30,15 @@
       end
     end
 
+    context 'when file is relative to the current directory' do
+      let(:file) { "#{Dir.pwd}/path/to/file" }
+
+      it 'reports offenses as error with the relative path' do
+        expect(output.string)
+          .to include('::error file=path/to/file,line=1,col=1::This is a message.')
+      end
+    end
+
     context 'when no offenses are detected' do
       let(:offenses) { [] }