testsuite: Add test for #21962

testsuite/tests/array/should_run/T21962.hs

+{-# LANGUAGE UnboxedTuples #-}
+{-# LANGUAGE MagicHash #-}
+
+module Main where
+
+import GHC.IO
+import GHC.Exts
+
+main :: IO ()
+main = do
+   IO $ \s0 -> case newArray# 0# () s0 of (# s1, arr #) -> (# s1, () #)

testsuite/tests/array/should_run/all.T

@@ -23,3 +23,4 @@ test('arr017', when(fast(), skip), compile_and_run, [''])
 test('arr018', when(fast(), skip), compile_and_run, [''])
 test('arr019', normal, compile_and_run, [''])
 test('arr020', normal, compile_and_run, [''])
+test('T21962', normal, compile_and_run, [''])