tests: config: Add type annotations.

[prah23]

What does this PR do?
Adds type annotations to the test_keys.py, test_themes.py and test_color.py files. Adds these files to the list in run-mypy.

Tested?

• Manually
• Existing tests (adapted, if necessary)
• Passed linting & tests (each commit)

Commit flow

• bugfix: tests: keys: Use lists for keys of key bindings.
  This commits replaces the data structure used for mentioning the keys
  of the various key bindings under test_commands_for_random_tips from
  set to list which is the right structure.

• refactor: tests: keys: Add type annotations.
  This commit adds parameter and return type annotations or hints
  to the test_keys.py file, that contains tests for its counterpart
  keys.py from the zulipterminal module, to make mypy checks
  consistent and improve code readability.

• tools: Include test_keys.py to be checked by mypy.
  This commit adds test_keys.py to the type_consistent_testfiles
  list to check for type consistency with mypy.
  Commits on Jul 25, 2021

• refactor: tests: themes: Add type annotations.
  This commit adds parameter and return type annotations or hints to the
  test_themes.py file, that contains tests for its counterpart
  themes.py from the zulipterminal module, to make mypy
  checks consistent and improve code readability.

• tools: Include test_themes.py to be checked by mypy.
  This commit adds test_themes.py to the type_consistent_testfiles
  list to check for type consistency with mypy.

• refactor: tests: color: Rename variable to avoid conflict with class.
  This commit renames the Color variable of test_color_properties
  to avoid conflict with the Color class, to the name color
  instead.

• refactor: tests: color: Add type annotations.
  This commit adds paramter and return type annotations or hints to the
  test_color.py file, that contains tests for it's counterpart
  color.py from the zulipterminal module, to make mypy checks
  consistent and improve code readability.

• tools: Include test_color.py to be checked by mypy.
  This commit adds test_color.py to the type_consistent_testfiles
  list to check for type consistency with mypy.

[neiljp]

@prah23 This was a good choice to group together 👍 zulipbot thinks this is "large", but I'm unconvinced ;) Some of the commits are tiny here again, but I'm OK with this for these changes, for consistency with other similar commits. I've removed a few uses of Any and updated your rename from color -> ExpandedColor (to use CamelCase for the enum), and other than a few minor commit text adjustments this is good to merge and I'll do so shortly 🎉

[zulipbot]

Hello @zulip/server-refactoring members, this pull request was labeled with the "area: refactoring" label, so you may want to check it out!