t2020: test variations that matter

Because our test suite is not about validating the working of the
shell, it is pointless to test variations of how a literal string
'yes' is quoted when assigned to an environment variable.

Instead, test various ways to spell 'yes' (we use strcasecmp() so
uppercased and capitalized variant should work just like 'yes'
spelled in all lowercase) and make sure we take them as 'yes'.  That
is more relevant in testing Git.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t2020-checkout-detach.sh

@@ -294,15 +294,15 @@ test_expect_success 'describe_detached_head does print SHA-1 ellipsis when asked
 	# Various ways of asking for ellipses...
 	# The user can just use any kind of quoting (including none).
 
-	GIT_PRINT_SHA1_ELLIPSIS="yes" git -c 'core.abbrev=12' checkout HEAD^ >actual 2>&1 &&
+	GIT_PRINT_SHA1_ELLIPSIS=yes git -c 'core.abbrev=12' checkout HEAD^ >actual 2>&1 &&
 	check_detached &&
 	test_i18ncmp 1st_detach actual &&
 
-	GIT_PRINT_SHA1_ELLIPSIS='yes' git -c 'core.abbrev=12' checkout HEAD^ >actual 2>&1 &&
+	GIT_PRINT_SHA1_ELLIPSIS=Yes git -c 'core.abbrev=12' checkout HEAD^ >actual 2>&1 &&
 	check_detached &&
 	test_i18ncmp 2nd_detach actual &&
 
-	GIT_PRINT_SHA1_ELLIPSIS=yes git -c 'core.abbrev=12' checkout HEAD^ >actual 2>&1 &&
+	GIT_PRINT_SHA1_ELLIPSIS=YES git -c 'core.abbrev=12' checkout HEAD^ >actual 2>&1 &&
 	check_detached &&
 	test_i18ncmp 3rd_detach actual &&