Bump the min Gradle requirement to 7.1 and test on 9.0.0-rc-1

[Goooler]

No description provided.

[nedtwigg]

• Good call! I'm fine with removing support for Java 11 Remove support for Java 11 #2375

[Goooler]

Will finish this later.

[Copilot]

Pull Request Overview

This PR raises the minimum supported Gradle version to 7.1, removes legacy pre-7.1 code paths, and updates CI and wrapper settings to test on Gradle 9.0.0-rc-1.

• Bump SpotlessPlugin’s VER_GRADLE_min from 6.1.1 to 7.1 and update related tests and error messages
• Remove legacy JavaPluginConvention/DslObject branches in JvmLang and GroovyExtension
• Update Gradle wrapper to 9.0.0-rc-1 and CI workflows to use Java 21 (with a secondary Java 11 build on Gradle 8.14)

Reviewed Changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
testlib/src/main/java/com/diffplug/spotless/TestProvisioner.java	updated exception handling
testlib/build.gradle	corrected project dependency reference
plugin-gradle/src/test/java/com/diffplug/gradle/spotless/SpotlessPluginRedirectTest.java	updated error message Gradle version
plugin-gradle/src/test/java/com/diffplug/gradle/spotless/NativeCmdIntegrationTest.java	removed specific Gradle version for config cache
plugin-gradle/src/test/java/com/diffplug/gradle/spotless/GradleIntegrationHarness.java	removed obsolete config cache enum
plugin-gradle/src/main/java/com/diffplug/gradle/spotless/SpotlessPlugin.java	bumped minimum Gradle version constants
plugin-gradle/src/main/java/com/diffplug/gradle/spotless/JvmLang.java	removed pre-7.1 legacy source set logic
plugin-gradle/src/main/java/com/diffplug/gradle/spotless/GroovyExtension.java	removed legacy GroovySourceSet code
plugin-gradle/CHANGES.md	added changelog entry for bumped Gradle requirement
lib/build.gradle	configured test discovery behavior for Gradle 9+
gradlew	updated copyright header
gradle/wrapper/gradle-wrapper.properties	upgraded wrapper to Gradle 9.0.0-rc-1
.github/workflows/deploy.yml	bumped setup-java to Java 21
.github/workflows/ci.yml	updated CI matrix Java versions and added Java 11 job
.github/workflows/changelog-print.yml	bumped setup-java to Java 21

Comments suppressed due to low confidence (3)

plugin-gradle/CHANGES.md:9

• The changelog entry is under '### Changed' without a version heading; add a new version section (e.g., '## [7.1.0] - YYYY-MM-DD') above this change to follow keepachangelog format.

### Changed

gradlew:4

• [nitpick] The copyright header was reduced to '2015' only—consider updating the year range to include 2025 or removing the end year consistently.

# Copyright © 2015 the original authors.

plugin-gradle/src/test/java/com/diffplug/gradle/spotless/NativeCmdIntegrationTest.java:56

• Removing the explicit withGradleVersion call will skip testing the configuration cache behavior; re-add the appropriate .withGradleVersion(...) to ensure this test runs against the intended Gradle version.

			return super.gradleRunner();

[Goooler]

This is a significant change; the next Gradle plugin release should be 7.1 or a similar version.