runtime/stringtable/StringTableCleaningTest.java fails on 32-bit platforms

Fails because it requests 3G heap:

$ CONF=linux-x86-server-fastdebug make images run-test TEST=runtime/stringtable/StringTableCleaningTest.java

STDERR:
 stdout: [[0.005s][info][gc] Using G1
Error occurred during initialization of VM
Could not reserve enough space for 3145728KB object heap
];
 stderr: []
 exitValue = 1

Testing if it can accept 1g instead.

Test is the new addition in 16 since JDK-8248391.