t4034: fix use of one-shot variable assignment with shell function

The behavior of a one-shot environment variable assignment of the form
"VAR=val cmd" is unspecified according to POSIX when "cmd" is a shell
function. Indeed the behavior differs between shell implementations and
even different versions of the same shell, thus should be avoided.

Signed-off-by: Eric Sunshine <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: sunshineco

t/t4034-diff-words.sh

@@ -70,7 +70,7 @@ test_language_driver () {
 		word_diff --color-words
 	'
 	test_expect_success "diff driver '$lang' in Islandic" '
-		LANG=is_IS.UTF-8 LANGUAGE=is LC_ALL="$is_IS_locale" \
+		test_env LANG=is_IS.UTF-8 LANGUAGE=is LC_ALL="$is_IS_locale" \
 		word_diff --color-words
 	'
 }