Fix pressing two keys with the same keycode but different modifiers (#2710)

Fix pressing two keys with the same keycode but different modifiers (#2710)

* Fix extra keyboard report during test_fixture teardown

* Add tests for pressing two keys with only different modifers

* Fix #1708

When two keys that use the same keycode, but different modifiers were
pressed at the same time, the second keypress wasn't registered. This is
fixed by forcing a key release when we detect a new press for the same
keycode.

* Fix the NKRO version of is_key_pressed

* Fix uninitalized loop variable

Co-authored-by: Jack Humbert <jack.humb@gmail.com>