jspace fails on i386 in `validate` flavour

While looking at !10957 (closed) I found that jspace has started failing on i386-linux when built in the validate flavour. For instance, see this job from master:

--- /dev/null	2023-12-14 09:43:55.029487578 +0000
+++ "/builds/ghc/ghc/tmp/ghctest-77brmygh/test   spaces/testsuite/tests/driver/j-space/jspace.run/jspace.run.stderr.normalised"	2023-12-14 10:31:20.667286768 +0000
@@ -0,0 +1,31 @@
+
+<no location info>:
+    panic! (the 'impossible' happened)
+  GHC version 9.9.20231214:
+	getRuntimeRep
+  'Many :: Multiplicity
+  Call stack:
+      CallStack (from HasCallStack):
+        callStackDoc, called at compiler/GHC/Utils/Panic.hs:<line>:<column> in <package-id>:GHC.Utils.Panic
+        pprPanic, called at compiler/GHC/Core/Type.hs:<line>:<column> in <package-id>:GHC.Core.Type
+  CallStack (from HasCallStack):
+    panic, called at compiler/GHC/Utils/Error.hs:<line>:<column> in <package-id>:GHC.Utils.Error
+
+
+Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug
+
+
+<no location info>:
+    panic! (the 'impossible' happened)
+  GHC version 9.9.20231214:
+	getRuntimeRep
+  'Many :: Multiplicity
+  Call stack:
+      CallStack (from HasCallStack):
+        callStackDoc, called at compiler/GHC/Utils/Panic.hs:<line>:<column> in <package-id>:GHC.Utils.Panic
+        pprPanic, called at compiler/GHC/Core/Type.hs:<line>:<column> in <package-id>:GHC.Core.Type
+  CallStack (from HasCallStack):
+    panic, called at compiler/GHC/Utils/Error.hs:<line>:<column> in <package-id>:GHC.Utils.Error
+
+
+Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug