Use mock context for ActionIntentExecutorTest

We don't actually want to start an intent.

Bug: 411311893
Fix: 411311893
Test: atest SystemUITests:com.android.systemui.screenshot.ActionIntentExecutorTest#launchIntent_callsCloseSystemWindows
Flag: EXEMPT test only
Change-Id: Ib6bcd6aae9cf9d00bc141ee914dde9b95ce2691f