Add test for T22671

This was fixed by b13c6ea5

Closes #22671

testsuite/tests/numeric/should_run/T22671.hs

+module Main where
+
+import Data.Bits
+import Control.Monad
+
+main :: IO ()
+main = unless (length (show (1 `shiftL` (1 `shiftL` 20) :: Integer)) == 315653)
+              (error "Incorrect result for bignum calculation")

testsuite/tests/numeric/should_run/all.T

@@ -79,4 +79,5 @@ test('IntegerToFloat', normal, compile_and_run, [''])
 
 test('T20291', normal, compile_and_run, [''])
 test('T22282', normal, compile_and_run, [''])
+test('T22671', normal, compile_and_run, [''])
 test('foundation', normal, compile_and_run, ['-O -package transformers'])