Assert motion action in A11yInputFilterInputTest

Besides making the test more strict, the real reason this change is
needed is because we are making 'withSource' matcher work with general
input events, and not only with motion events. The addition of this
"withMotionAction" matcher will help compiler deduce the overall type
correctly, and allow us to match against motionevents later.

Bug: 439992405
Test: atest AccessibilityInputFilterInputTest
Flag: EXEMPT TEST_ONLY
Change-Id: Ib05a2224c220450dd76a259e7d01a3b535f6da2d