Bump org.spockframework:spock-core in /test-project-groovy

Bumps [org.spockframework:spock-core](https://github.com/spockframework/spock) from 2.4-M1-groovy-3.0 to 2.4-M6-groovy-4.0.
- [Release notes](https://github.com/spockframework/spock/releases)
- [Changelog](https://github.com/spockframework/spock/blob/master/docs/release_notes.adoc)
- [Commits](https://github.com/spockframework/spock/commits)

---
updated-dependencies:
- dependency-name: org.spockframework:spock-core
  dependency-version: 2.4-M6-groovy-4.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

test-project-groovy/build.gradle

@@ -31,7 +31,7 @@ subprojects {
         testImplementation "org.junit.jupiter:junit-jupiter-params:$jUnitVersion"
         testImplementation "org.junit.jupiter:junit-jupiter-engine:$jUnitVersion"
         testRuntimeOnly "org.junit.platform:junit-platform-launcher:$jUnitPlatformVersion"
-        testImplementation("org.spockframework:spock-core:2.4-M1-groovy-3.0") {
+        testImplementation("org.spockframework:spock-core:2.4-M6-groovy-4.0") {
             exclude module: 'groovy-nio'
             exclude module: 'groovy-test'
             exclude module: 'groovy-xml'