Change image attachment test to use a public resource ID

The test started failing due to resource ID issues when new resources were added likely because test APK resource IDs became out of sync. Because this test doesn't care about what image it's using (just that it's an image), using a public drawable resource is likely more stable and less susceptible to this issue.

Bug: 249302567
Test: atest RemoteInputViewTest
Change-Id: Icb68affe4ecabeb363d97e8517d2acd8e8031d65