Update pull_request.yml to stop the 6.1 release builds

Author: finagolfin

.github/workflows/pull_request.yml

@@ -40,9 +40,6 @@ jobs:
          swift-version: ['release', 'swift-6.2-branch', 'development']
          # add docker-specific variants that run the compiler validation tests
          include:
-           - swift-version: 'release'
-             build-type: 'docker'
-             build-compiler: '1'
            - swift-version: 'swift-6.2-branch'
              build-type: 'docker'
              build-compiler: '1'