patch 8.2.1526: line in testdir Makefile got commented out

Problem:    Line in testdir Makefile got commented out. (Christian Brabandt)
Solution:   Revert.
diff --git a/src/testdir/Makefile b/src/testdir/Makefile
index 6431f6a..2fb329a 100644
--- a/src/testdir/Makefile
+++ b/src/testdir/Makefile
@@ -12,7 +12,7 @@
 # Comment out this line to see the verbose output of tests.
 #
 # Catches SwapExists to avoid hanging at the ATTENTION prompt.
-#REDIR_TEST_TO_NULL = --cmd 'au SwapExists * let v:swapchoice = "e"' > /dev/null
+REDIR_TEST_TO_NULL = --cmd 'au SwapExists * let v:swapchoice = "e"' > /dev/null
 
 # Uncomment this line to use valgrind for memory leaks and extra warnings.
 #   The output goes into a file "valgrind.testN"