Remove unnecessary actions/setup-java

[eregon]

• See discussion on Fix JRuby CI for Windows #151

[eregon]

@headius @kou It's still failing
https://github.com/ruby/strscan/actions/runs/14857152857/job/41713119316?pr=155

 mkdir -p tmp/java/strscan
javac -target 1.8 -source 1.8 -Xlint -d tmp/java/strscan -cp D:/jruby-10.0.0.0/lib/jruby.jar ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java ext/jruby/org/jruby/ext/strscan/StringScannerLibrary.java
ext\jruby\org\jruby\ext\strscan\RubyStringScanner.java:36: error: cannot access Ruby
import org.jruby.Ruby;
                ^
  bad class file: D:\jruby-10.0.0.0\lib\jruby.jar(org/jruby/Ruby.class)
    class file has wrong version 65.0, should be 52.0
    Please remove or make sure it appears in the correct subdirectory of the classpath.
rake aborted!
Command failed with status (1): [javac -target 1.8 -source 1.8 -Xlint -d tmp/java/strscan -cp D:/jruby-10.0.0.0/lib/jruby.jar ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java ext/jruby/org/jruby/ext/strscan/StringScannerLibrary.java]
D:/a/strscan/strscan/vendor/bundle/jruby/3.4.0/gems/rake-compiler-1.3.0/lib/rake/javaextensiontask.rb:129:in 'block in define_compile_tasks'
org/jruby/ext/monitor/Monitor.java:85:in 'synchronize'
org/jruby/ext/monitor/Monitor.java:85:in 'synchronize'
org/jruby/ext/monitor/Monitor.java:85:in 'synchronize'
org/jruby/ext/monitor/Monitor.java:85:in 'synchronize'
org/jruby/ext/monitor/Monitor.java:85:in 'synchronize'
org/jruby/ext/monitor/Monitor.java:85:in 'synchronize'
D:/a/strscan/strscan/vendor/bundle/jruby/3.4.0/gems/rake-13.2.1/exe/rake:27:in '<main>'
D:\a\strscan\strscan\vendor\bundle\jruby\3.4.0\bin\rake:25:in '<main>'
Tasks: TOP => compile => compile:java => compile:strscan:java => copy:strscan:java => tmp/java/strscan/strscan.jar => tmp/java/strscan/.build
(See full trace by running task with --trace)

Maybe it's #151 (comment) (I don't have a Windows machine to check) or maybe it's the -target 1.8 -source 1.8 which sounds potentially problematic since JRuby 10 is Java 21+ (but then that should fail when setup-java is used too, so probably not the issue).

[kou]

@headius Does JRuby on Windows have RbConfig::CONFIG["EXEEXT"] = ".exe"?