Update dependency org.apache.maven.plugins:maven-gpg-plugin to v3.2.8

Author: renovate[bot]

sigstore-maven-plugin/build.gradle.kts

@@ -15,7 +15,7 @@ dependencies {
 
     implementation(project(":sigstore-java"))
     implementation("org.bouncycastle:bcutil-jdk18on:1.80")
-    implementation("org.apache.maven.plugins:maven-gpg-plugin:3.2.7")
+    implementation("org.apache.maven.plugins:maven-gpg-plugin:3.2.8")
 
     testImplementation("org.apache.maven.shared:maven-verifier:1.8.0")