Upgrade to proto 3.21.8

Bug: 255753711
Test: ./gradlew tasks

Change-Id: I22847dccb84f2e8f870c59602f6c8317f298c35f
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index 54cd813..94ad317 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -46,7 +46,7 @@
 metalava = "1.0.0-alpha06"
 mockito = "2.25.0"
 moshi = "1.13.0"
-protobuf = "3.19.4"
+protobuf = "3.21.8"
 paparazzi = "1.0.0"
 paparazziNative = "2022.1.1-canary-f5f9f71"
 skiko = "0.7.7"