Fix reproducible build test, a none legacy test for this should be added at a later date.

src/test/resources/projects/reproducible/build.gradle

@@ -10,6 +10,12 @@ archivesBaseName = project.archives_base_name
 version = project.mod_version
 group = project.maven_group
 
+loom {
+	mixin {
+		useLegacyMixinAp = true
+	}
+}
+
 dependencies {
 	minecraft "com.mojang:minecraft:${project.minecraft_version}"
 	mappings "net.fabricmc:yarn:${project.yarn_mappings}:v2"