deps: update docker.io/library/alpine docker tag to v3.21.1 (#3551)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| docker.io/library/alpine | stage | patch | `3.21.0` -> `3.21.1` |

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Co-authored-by: Min Zhu <[email protected]>

.cloudbuild/library_generation/library_generation.Dockerfile

@@ -27,7 +27,7 @@ RUN mvn install -B -ntp -DskipTests -Dclirr.skip -Dcheckstyle.skip
 RUN cp "/root/.m2/repository/com/google/api/gapic-generator-java/${DOCKER_GAPIC_GENERATOR_VERSION}/gapic-generator-java-${DOCKER_GAPIC_GENERATOR_VERSION}.jar" \
   "./gapic-generator-java.jar"
 
-FROM docker.io/library/alpine:3.21.0@sha256:21dc6063fd678b478f57c0e13f47560d0ea4eeba26dfc947b2a4f81f686b9f45 as glibc-compat
+FROM docker.io/library/alpine:3.21.1@sha256:b97e2a89d0b9e4011bb88c02ddf01c544b8c781acf1f4d559e7c8f12f1047ac3 as glibc-compat
 
 RUN apk add git sudo
 # This SHA is the latest known-to-work version of this binary compatibility tool