`java-17-plus` profile in `pom.xml` incorrectly loads Error Prone version requiring Java 21

The java-17-plus profile in pom.xml:520 activates on <jdk>[17,)</jdk> and puts -Xplugin:ErrorProne on the javac command line, pulling error_prone_core 2.50.0 from pom.xml:555. The classes in that jar, ErrorProneJavacPlugin.class among them, are compiled to class file version 65, which is Java 21. On JDK 17 or 18 through 20 the profile switches on but javac cannot load the plugin, so compile fails before any source file is touched, with nothing but a defineClass1 stack trace.

This contradicts README.md:184-188, which asks for "Java 11+" and says error-prone runs with "Java 17+". A contributor who follows the README on JDK 17 cannot run mvn clean install -Pqulice at all. Switching the profile off by hand does not rescue them either: src/test/java/fixtures/FixPack.java:90 casts this.pack.get("sheets") from Object to List<String> unchecked, and with failOnWarning set that warning becomes a compilation error in testCompile.

Changing the activation to <jdk>[21,)</jdk> and the README line to "Java 21+" makes the promise match the plugin. The cast in FixPack.java:90 should also go, so the build compiles cleanly whenever the profile is off.

@yegor256