Replace broken references to CircleCI (#1318)

buildSrc/src/main/kotlin/pklPublishLibrary.gradle.kts

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -54,8 +54,8 @@ publishing {
           url.set("https://github.com/apple/pkl/issues")
         }
         ciManagement {
-          system.set("Circle CI")
-          url.set("https://app.circleci.com/pipelines/github/apple/pkl")
+          system.set("GitHub Actions")
+          url.set("https://github.com/apple/pkl/actions")
         }
       }
     }