Building release app with skip-keychain raises error: "Missing classes detected while running R8" for com.google.errorprone.annotations.Immutable

[marcprux]

The following error will occur when building an app that depends on skip-keychain in release mode (e.g., using fastlane assemble from the Android/ folder):

ERROR: Missing classes detected while running R8. Please add the missing classes or apply additional keep rules that are generated in /opt/src/github/skiptools/skipapp-notes/.build/Android/app/outputs/mapping/release/missing_rules.txt.
ERROR: R8: Missing class com.google.errorprone.annotations.Immutable (referenced from: com.google.crypto.tink.KeyTemplate and 11 other contexts)

> Task :app:minifyReleaseWithR8 FAILED
w: Detected multiple Kotlin daemon sessions at 
[Incubating] Problems report is available at: file:///opt/src/github/skiptools/skipapp-notes/.build/Android/skip.notes/reports/problems/problems-report.html

This is reported at tink-crypto/tink-java#7. The recommended workaround to add the following rules to the Android/app/proguard-rules.pro file seems to work:

-dontwarn com.google.errorprone.annotations.CanIgnoreReturnValue
-dontwarn com.google.errorprone.annotations.Immutable