remove deprecated 6.1 nightly

Author: sebsto

.github/workflows/pull_request.yml

@@ -25,7 +25,7 @@ jobs:
       linux_5_9_enabled: false
       linux_5_10_enabled: false
       linux_6_0_enabled: true
-      linux_nightly_6_1_enabled: true
+      # this currently resolves to 6.1 nightly
       linux_nightly_next_enabled: true
       # this currently resolves to 6.2.dev
       # It crashes some of our tests https://github.com/swift-server/swift-aws-lambda-runtime/issues/509