Fix 'python-info-docstring-p' bug in the 2nd line of a buffer

Fix 'python-info-docstring-p' bug in the 2nd line of a buffer

* lisp/progmodes/python.el (python-info-docstring-p): Add
'looking-at-p' check when bobp.
* test/lisp/progmodes/python-tests.el (python-font-lock-operator-1)
(python-font-lock-operator-2): Restoration of ERTs deleted by
mistake.
(python-font-lock-escape-sequence-bytes-newline)
(python-font-lock-escape-sequence-hex-octal)
(python-font-lock-escape-sequence-unicode)
(python-font-lock-raw-escape-sequence): Change 'font-lock-doc-face'
to 'font-lock-string-face' and remove :expected-result :failed.
(python-info-docstring-p-8): New test.  (Bug#68284)