gh-151335: Add test for string with digits and whitespaces in test_isdigit()

[manoj-marimuthu]

The following PR adds a test case for test_isdigit() in Lib/test/string_tests.py to test strings with only digits and whitespaces.

self.checkequal(False, '123 ', 'isdigit')

• Issue: Test edge case in isdigit() method #151335

[StanFromIreland]

This adds no new coverage, there is nothing special about whitespace:

cpython/Objects/unicodeobject.c

Lines 12054 to 12057 in 8c0e251

	for (i = 0; i < length; i++) {
	if (!Py_UNICODE_ISDIGIT(PyUnicode_READ(kind, data, i)))
	Py_RETURN_FALSE;
	}

I see you have submitted several such PRs that add a single assert, I suggest you try fixing one of the open issues instead.

[bedevere-app]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.