testsuite: Add test for #25560

testsuite/tests/rts/T25560.hs

+import GHC.Conc
+
+main :: IO ()
+main = setNumCapabilities 100000

testsuite/tests/rts/T25560.stderr

+T25560: Uncaught exception ghc-internal:GHC.Internal.IO.Exception.IOException:
+
+user error (setNumCapabilities: This GHC build only supports up to 1 capabilities)

testsuite/tests/rts/all.T

@@ -630,3 +630,4 @@ test('T24142', [req_target_smp], compile_and_run, ['-threaded -with-rtsopts "-N2
 
 test('T25232', [unless(have_profiling(), skip), only_ways(['normal','nonmoving','nonmoving_prof','nonmoving_thr_prof']), extra_ways(['nonmoving', 'nonmoving_prof'] + (['nonmoving_thr_prof'] if have_threaded() else []))], compile_and_run, [''])
 test('T25280', [unless(opsys('linux'),skip),req_process,js_skip], compile_and_run, [''])
+test('T25560', exit_code(1), compile_and_run, [''])