[MagicAction] Update the button UI to address feedback from UX.

Changes
- Change the button text font
- Change the background color to be transparent

Bug: 383567383
Test: atest SmartActionScreenshotTest
Flag: com.android.systemui.notification_magic_actions_treatment
Change-Id: I2924d1fa9fde79759eab20169f46569f3b0d909c