Update components/microsoft_excel/sources/common/base-webhook.mjs

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

Author: michelle0927

components/microsoft_excel/sources/common/base-webhook.mjs

@@ -95,9 +95,10 @@ export default {
         status: 200,
         body: query.validationToken,
         headers: {
-          "content-type": "text/plan",
+          "content-type": "text/plain",
         },
       });
+    }
       return;
     }