slow validate: UnliftedTVar2 different results

Reproduce with

hadrian/build test --freeze1  --docs=none --flavour=slow-validate --test-speed=slow --only="UnliftedTVar2"

Looks pretty worrying...

+++ "/run/user/1000/ghctest-derda1up/test   spaces/testsuite/tests/primops/should_run/UnliftedTVar2.run/UnliftedTVar2.run.stdout.normalised"	2022-08-05 18:31:49.508351218 +0100
@@ -1 +1 @@
-(True,True)
+(False,False)
*** unexpected failure for UnliftedTVar2(threaded2)
Actual stdout output differs from expected:
--- "/run/user/1000/ghctest-derda1up/test   spaces/testsuite/tests/primops/should_run/UnliftedTVar2.run/UnliftedTVar2.stdout.normalised"	2022-08-05 18:31:50.083327436 +0100
+++ "/run/user/1000/ghctest-derda1up/test   spaces/testsuite/tests/primops/should_run/UnliftedTVar2.run/UnliftedTVar2.run.stdout.normalised"	2022-08-05 18:31:50.083327436 +0100
@@ -1 +1 @@
-(True,True)
+(False,True)
*** unexpected failure for UnliftedTVar2(nonmoving_thr)
Actual stdout output differs from expected:
--- "/run/user/1000/ghctest-derda1up/test   spaces/testsuite/tests/primops/should_run/UnliftedTVar2.run/UnliftedTVar2.stdout.normalised"	2022-08-05 18:31:50.790298195 +0100
+++ "/run/user/1000/ghctest-derda1up/test   spaces/testsuite/tests/primops/should_run/UnliftedTVar2.run/UnliftedTVar2.run.stdout.normalised"	2022-08-05 18:31:50.790298195 +0100
@@ -1 +1 @@
-(True,True)
+(False,True)
*** unexpected failure for UnliftedTVar2(nonmoving_thr_sanity)

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