Make the migration template typed

Signed-off-by: Joas Schilling <coding@schilljs.com>

core/Command/Db/Migrations/GenerateCommand.php

@@ -60,7 +60,7 @@ class {{classname}} extends SimpleMigrationStep {
 	 * @param Closure $schemaClosure The `\Closure` returns a `ISchemaWrapper`
 	 * @param array $options
 	 */
-	public function preSchemaChange(IOutput $output, Closure $schemaClosure, array $options) {
+	public function preSchemaChange(IOutput $output, Closure $schemaClosure, array $options): void {
 	}
 
 	/**
@@ -69,7 +69,7 @@ class {{classname}} extends SimpleMigrationStep {
 	 * @param array $options
 	 * @return null|ISchemaWrapper
 	 */
-	public function changeSchema(IOutput $output, Closure $schemaClosure, array $options) {
+	public function changeSchema(IOutput $output, Closure $schemaClosure, array $options): ?ISchemaWrapper {
 {{schemabody}}
 	}
 
@@ -78,7 +78,7 @@ class {{classname}} extends SimpleMigrationStep {
 	 * @param Closure $schemaClosure The `\Closure` returns a `ISchemaWrapper`
 	 * @param array $options
 	 */
-	public function postSchemaChange(IOutput $output, Closure $schemaClosure, array $options) {
+	public function postSchemaChange(IOutput $output, Closure $schemaClosure, array $options): void {
 	}
 }
 ';