Fix spurious failure of the check/all script (quantumlib#6611)

- Avoid passing an empty string argument to `check/format-incremental`
  when invoked from `check/all`

- Improve validation of the git-revision argument in check scripts by
  allowing git tags that resolve to a commit

- Fix invalid use of `?` in egrep pattern

- Make check/mypy pass in the dev.env.txt virtual environment

Author: pavoljuhas

cirq/contrib/svg/svg_test.py

@@ -1,5 +1,5 @@
 # pylint: disable=wrong-or-nonexistent-copyright-notice
-import IPython.display  # type: ignore
+import IPython.display
 import numpy as np
 import pytest