Upgrades Gradle Plugin Publish plugin (#7005)

- Updates the Gradle Plugin Publish plugin (attempted by #6663)
- Fixes #6628 by upgrading, as mentioned in
[gradle/gradle#19331](gradle/gradle#19331)

gradle-plugins/build.gradle.kts

@@ -137,15 +137,14 @@ afterEvaluate {
       }
     }
   }
+}
 
 // Sign only if we have a key to do so
-  val signingKey: String? = System.getenv("GPG_PRIVATE_KEY")
-// Stub out entire signing block off of CI since Gradle provides no way of lazy configuration of
-// signing tasks.
-  if (System.getenv("CI") != null && signingKey != null) {
-    signing {
-      useInMemoryPgpKeys(signingKey, System.getenv("GPG_PASSWORD"))
-      sign(publishing.publications["pluginMaven"])
-    }
-  }
+val signingKey: String? = System.getenv("GPG_PRIVATE_KEY")
+signing {
+  setRequired({
+    // only require signing on CI and when a signing key is present
+    System.getenv("CI") != null && signingKey != null
+  })
+  useInMemoryPgpKeys(signingKey, System.getenv("GPG_PASSWORD"))
 }

gradle-plugins/settings.gradle.kts

@@ -1,6 +1,6 @@
 pluginManagement {
   plugins {
-    id("com.gradle.plugin-publish") version "0.15.0"
+    id("com.gradle.plugin-publish") version "1.0.0"
     id("io.github.gradle-nexus.publish-plugin") version "1.1.0"
   }
 }