Java 21 throws UnsupportedOperationException when setSecurityManager() is called without passing -Djava.security.manager=... property.

This causes jtreg self-test failures such as:
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/bin/grep -s 'Test results: passed: 18; failed: 2' /<<PKGBUILDDIR>>/build/test/BadTests.othervm/jt.log > /dev/null
make[2]: *** [../test/badtests/BadTests.gmk:38: /<<PKGBUILDDIR>>/build/test/BadTests.othervm.ok] Error 1
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caused by an extra failure in ExitTest:
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ExitTest.java#id1 Failed. Execution failed: `main' threw exception: java.lang.UnsupportedOperationException: The Security Manager is deprecated and will be removed in a future release
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Tests that fail:
- test/BadTests.othervm
- test/SecurityManager