Updated diff to show \t in string comparison assertions

[mthaitan]

Closes #10704

Added "\t" characters to the diff message, did not add "\n" because the diff already creates each line on a separate line and it shows in the "AssertionError: ______" section of the error message.
Updated test suite to reflect this change.

Before:

After:

pytest.param(
        """
        def test_this():
            result =   '''spam    bacon
            eggs love'''
            desired = "spam bacon eggs love"
            assert result == desired
        """,
        """
        >       assert result == desired
        E       AssertionError: assert 'spam    bacon\\n    eggs love' == 'spam bacon eggs love'
        E         - spam bacon eggs love
        E         + spam\\tbacon
        E         + \\teggs love
        """,
        id='Test "not in" string',
    ),

Worked with @egwetzel on this issue in team with @HSamiul.

[Zac-HD]

This looks wrong to me - there are no tab characters in the original strings, so we're actually lying about the contents by replacing four spaces!

I think we need a different approach, perhaps showing the repr of the explanation lines in question if they differ in their trailing whitespace; or maybe only showing that for the trailing whitespace in question. Check out what the short summary does I guess?