test-lib-functions.sh: fix test_grep fail message wording

In the recent commit 2e87fca (test framework: further deprecate
test_i18ngrep, 2023-10-31), the test_i18ngrep function was
deprecated, and all the callers were updated to call the test_grep
function instead.  But test_grep inherited an error message that
still refers to test_i18ngrep by mistake.  Correct it so that a
broken call to the test_grep will identify itself as such.

Signed-off-by: Shreyansh Paliwal <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: shreyp135

t/test-lib-functions.sh

@@ -1222,7 +1222,7 @@ test_grep () {
 	if test $# -lt 2 ||
 	   { test "x!" = "x$1" && test $# -lt 3 ; }
 	then
-		BUG "too few parameters to test_i18ngrep"
+		BUG "too few parameters to test_grep"
 	fi
 
 	if test "x!" = "x$1"