Fix proguard rules for androidx.startup.

Fixes: b/186797694
Test: ./gradlew :work:integration-tests:testapp:assembleRelease
Change-Id: I1b3211970a7c7cbb5bf6b8c2bb61193f4a00bce6
diff --git a/startup/startup-runtime/proguard-rules.pro b/startup/startup-runtime/proguard-rules.pro
index b1048d8..961a1eb 100644
--- a/startup/startup-runtime/proguard-rules.pro
+++ b/startup/startup-runtime/proguard-rules.pro
@@ -5,4 +5,4 @@
     <init>();
 }
 
--assumenosideeffects class androidx.startup.StartupLogger
+-assumenosideeffects class androidx.startup.StartupLogger { public static <methods>; }