gradle: Add workaround for Dokka metaspace usage

Work around https://github.com/Kotlin/dokka/issues/1405 to fix builds on
GitHub Actions.
diff --git a/gradle.properties b/gradle.properties
index c6a3706..846e8a4 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -3,3 +3,6 @@
 kotlin.native.enableDependencyPropagation=false
 kotlin.js.generate.executable.default=false
 kotlin.mpp.stability.nowarn=true
+
+# Workaround for Dokka issue: https://github.com/Kotlin/dokka/issues/1405
+org.gradle.jvmargs=-XX:MaxMetaspaceSize=512m