Fix ProGuard configuration for 2.13

Note: We only support pro-guard on a best effort basis,
and developers should use R8 whenever possible.

#minor-release

PiperOrigin-RevId: 355129695

library/common/proguard-rules.txt

@@ -16,3 +16,7 @@
 -dontwarn com.google.errorprone.annotations.**
 -dontwarn com.google.j2objc.annotations.**
 -dontwarn org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement
+
+# Workaround for https://issuetracker.google.com/issues/112297269
+# This is needed for ProGuard but not R8.
+-keepnames class com.google.common.base.Function { *; }