SubmittingPatches: clarify GitHub visual

GitHub has two general forms for its states, sometimes they're a simple
colored object (e.g. green check or red x), and sometimes there's also a
colored container (e.g. green box or red circle) which contains that
object (e.g. check or x).

That's a lot of words to try to describe things, but in general, the key
for a failure is that it's recognized as an `x` and that it's associated
with the color red -- the color of course is problematic for people who
are red-green color-blind, but that's why they are paired with distinct
shapes.

Signed-off-by: Josh Soref <jsoref@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/SubmittingPatches

@@ -602,11 +602,11 @@ After the initial setup, CI will run whenever you push new changes
 to your fork of Git on GitHub.  You can monitor the test state of all your
 branches here: `https://github.com/<Your GitHub handle>/git/actions/workflows/main.yml`
 
-If a branch did not pass all test cases then it is marked with a red
-cross. In that case you can click on the failing job and navigate to
-"ci/run-build-and-tests.sh" and/or "ci/print-test-failures.sh". You
-can also download "Artifacts" which are tarred (or zipped) archives
-with test data relevant for debugging.
+If a branch does not pass all test cases then it will be marked with a
+red +x+, instead of a green check. In that case, you can click on the
+failing job and navigate to "ci/run-build-and-tests.sh" and/or
+"ci/print-test-failures.sh". You can also download "Artifacts" which
+are tarred (or zipped) archives with test data relevant for debugging.
 
 Then fix the problem and push your fix to your GitHub fork. This will
 trigger a new CI build to ensure all tests pass.