Align empty module declaration with TS (#19568)

changelog_unreleased/flow/19568.md

@@ -0,0 +1,14 @@
+#### Stop enforcing empty module declaration to break (#19568 by @fisker)
+
+<!-- prettier-ignore -->
+```flow
+// Input
+declare module "foo" {}
+
+// Prettier stable
+declare module "foo" {
+}
+
+// Prettier main
+declare module "foo" {}
+```