todo-backend: switch OpenApi schema to 3.0.3

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

plugins/todo-backend/src/schema/openapi.generated.ts

@@ -19,7 +19,7 @@
 // ******************************************************************
 
 export default {
-  openapi: '3.1.0',
+  openapi: '3.0.3',
   info: {
     title: '@backstage/plugin-todo-backend',
     version: '1',

plugins/todo-backend/src/schema/openapi.yaml

@@ -1,4 +1,4 @@
-openapi: 3.1.0
+openapi: 3.0.3
 
 info:
   title: '@backstage/plugin-todo-backend'