Use Ruby 3.1 for linters

Author: PowerKiKi

Diff for: .github/workflows/brakeman.yml

@@ -25,7 +25,7 @@ jobs:
     - name: Setup Ruby
       uses: ruby/setup-ruby@v1
       with:
-        ruby-version: 2.6
+        ruby-version: 3.1
         bundler-cache: true
 
     - name: Setup gems

Diff for: .github/workflows/rubocop.yml

@@ -25,7 +25,7 @@ jobs:
     - name: Setup Ruby
       uses: ruby/setup-ruby@v1
       with:
-        ruby-version: 2.6
+        ruby-version: 3.1
         bundler-cache: true
 
     - name: Setup gems