testsuite: Don't run T15892 in nonmoving ways

The nonmoving GC doesn't support `+RTS -G1`, which this test insists on.

testsuite/tests/codeGen/should_run/all.T

@@ -194,9 +194,11 @@ test('T15696_3', normal, compile_and_run, ['-O'])
 
 test('T15892',
      [ ignore_stdout,
-        # we want to do lots of major GC to make the bug more likely to
-        # happen, so -G1 -A32k:
-        extra_run_opts('+RTS -G1 -A32k -RTS') ],
+       # -G1 is unsupported by the nonmoving GC
+       omit_ways(['nonmoving', 'nonmoving_thr']),
+       # we want to do lots of major GC to make the bug more likely to
+       # happen, so -G1 -A32k:
+       extra_run_opts('+RTS -G1 -A32k -RTS') ],
      compile_and_run, ['-O'])
 test('T16617', normal, compile_and_run, [''])
 test('T16449_2', exit_code(0), compile_and_run, [''])