JavaScript: T16135 panics

While working on !10576 (closed), once perf tests were re-enabled this test began to fail:

--- "/builds/ghc/ghc/tmp/ghctest-tlsvhdhr/test   spaces/testsuite/tests/ado/T16135.run/T16135.stderr.normalised"	2023-06-08 19:42:51.271247625 +0000
+++ "/builds/ghc/ghc/tmp/ghctest-tlsvhdhr/test   spaces/testsuite/tests/ado/T16135.run/T16135.comp.stderr.normalised"	2023-06-08 19:42:51.271247625 +0000
@@ -1,14 +1,13 @@
-T16135.hs:11:18: [GHC-83865]
-     Couldn't match type ‘a0’ with ‘a’
-      Expected: f a0
-        Actual: f a
-      ‘a’ is a rigid type variable bound by
-        a pattern with constructor:
-          MkT :: forall {k} (f :: k -> *) (a :: k). f a -> T f,
-        in a pattern binding in
-             a 'do' block
-        at T16135.hs:10:5-10
-     In the first argument of ‘MkT’, namely ‘fa’
-      In the second argument of ‘($)’, namely ‘MkT fa’
-      In a stmt of a 'do' block: return $ MkT fa
-     Relevant bindings include fa :: f a (bound at T16135.hs:10:9)
+ghc: panic! (the 'impossible' happened)
+  GHC version 9.7.20230607:
+	ASSERT failed!
+  a0_ay9[tau:1]
+  1
+  Call stack:
+      CallStack (from HasCallStack):
+        assertPpr, called at compiler/GHC/Tc/Errors.hs:<line>:<column> in <package-id>:GHC.Tc.Errors
+  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