Switch CI pipeline to a JDK17 baseline

This commit introduces a new `spring-framework-6.0.x` CI pipeline with
JDK 17 baseline.

Note that Kotlin still uses a JDK11 baseline for now, this will be
addressed in gh-27413.

Closes gh-27409

ci/scripts/check-project.sh

@@ -4,6 +4,6 @@ set -e
 source $(dirname $0)/common.sh
 
 pushd git-repo > /dev/null
-./gradlew -Dorg.gradle.internal.launcher.welcomeMessageEnabled=false -Porg.gradle.java.installations.fromEnv=JDK11,JDK15 \
+./gradlew -Dorg.gradle.internal.launcher.welcomeMessageEnabled=false -Porg.gradle.java.installations.fromEnv=JDK17 \
   -PmainToolchain=${MAIN_TOOLCHAIN} -PtestToolchain=${TEST_TOOLCHAIN} --no-daemon --max-workers=4 check
 popd > /dev/null