t6038: make tests fail for the right reason

t6038 had a pair of tests that were expected to fail, but weren't
failing for the expected reason.  Both were meant to do a merge that
could be done cleanly after renormalization, but were supposed to fail
for lack of renormalization.  Unfortunately, both tests had staged
changes, and checkout -m would abort due to the presence of those staged
changes before even attempting a merge.

Fix this first issue by utilizing git-restore instead of git-checkout,
so that the index is left alone and just the working directory gets the
changes we want.

However, there is a second issue with these tests.  Technically, they
just wanted to verify that after renormalization, no conflicts would be
present.  This could have been checked for by grepping for a lack of
conflict markers, but the test instead tried to compare the working
directory files to an expected result.  Unfortunately, the setting of
"text=auto" without setting core.eol to any value meant that the content
of the file (in particular, the line endings) would be
platform-dependent and the tests could only pass on some platforms.
Replace the existing comparison with a call to 'git diff --no-index
--ignore-cr-at-eol' to verify that the contents, other than possible
carriage returns in the file, match the expected results and in
particular that the file has no conflicts from the checkout -m
operation.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t6038-merge-text-auto.sh

@@ -168,9 +168,9 @@ test_expect_failure 'checkout -m after setting text=auto' '
 	git rm -fr . &&
 	rm -f .gitattributes &&
 	git reset --hard initial &&
-	git checkout a -- . &&
+	git restore --source=a -- . &&
 	git checkout -m b &&
-	compare_files expected file
+	git diff --no-index --ignore-cr-at-eol expected file
 '
 
 test_expect_failure 'checkout -m addition of text=auto' '
@@ -183,9 +183,9 @@ test_expect_failure 'checkout -m addition of text=auto' '
 	git rm -fr . &&
 	rm -f .gitattributes file &&
 	git reset --hard initial &&
-	git checkout b -- . &&
+	git restore --source=b -- . &&
 	git checkout -m a &&
-	compare_files expected file
+	git diff --no-index --ignore-cr-at-eol expected file
 '
 
 test_expect_failure 'cherry-pick patch from after text=auto was added' '