Only run Gradle compatibility tests against minimum and maximum release (#898)

Currently, we run against every release version, which is taking 20
minutes to run in CI, and this will grow as Gradle creates more
releases.

This limits the amount of Gradle versions being tested against;
theoretically, only testing against the minimum version and the maximum
version should ensure that we are compatible with every version in the
range.

buildSrc/src/main/kotlin/pklGradlePluginTest.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.
@@ -27,20 +27,23 @@ tasks.addRule("Pattern: compatibilityTest[All|Releases|Latest|Candidate|Nightly|
         dependsOn(
           "compatibilityTestReleases",
           "compatibilityTestCandidate",
-          "compatibilityTestNightly"
+          "compatibilityTestNightly",
         )
       }
     // releases in configured range
     "Releases" ->
       task("compatibilityTestReleases") {
         val versionInfos = GradleVersionInfo.fetchReleases()
-        val versionsToTestAgainst =
-          versionInfos.filter { versionInfo ->
-            val v = versionInfo.gradleVersion
-            !versionInfo.broken &&
-              v in gradlePluginTests.minGradleVersion..gradlePluginTests.maxGradleVersion &&
-              v !in gradlePluginTests.skippedGradleVersions
-          }
+        val allVersions =
+          versionInfos
+            .filter { versionInfo ->
+              val v = versionInfo.gradleVersion
+              !versionInfo.broken &&
+                v in gradlePluginTests.minGradleVersion..gradlePluginTests.maxGradleVersion &&
+                v !in gradlePluginTests.skippedGradleVersions
+            }
+            .sortedBy { it.gradleVersion }
+        val versionsToTestAgainst = listOf(allVersions.first(), allVersions.last())
 
         dependsOn(versionsToTestAgainst.map { createCompatibilityTestTask(it) })
       }
@@ -79,7 +82,7 @@ tasks.addRule("Pattern: compatibilityTest[All|Releases|Latest|Candidate|Nightly|
     else ->
       createCompatibilityTestTask(
         taskNameSuffix,
-        "https://services.gradle.org/distributions-snapshots/gradle-$taskNameSuffix-bin.zip"
+        "https://services.gradle.org/distributions-snapshots/gradle-$taskNameSuffix-bin.zip",
       )
   }
 }