fix: don't cache POST when serving embedded static html (#2766)

Author: pieh

src/run/headers.ts

@@ -279,6 +279,7 @@ export const setCacheControlHeaders = (
 
   if (
     cacheControl === null &&
+    ['GET', 'HEAD'].includes(request.method) &&
     !headers.has('cdn-cache-control') &&
     !headers.has('netlify-cdn-cache-control') &&
     requestContext.usedFsReadForNonFallback