qol(runtime): clarify message about unavailable headers (#10583)

* qol(runtime): clarify message about unavailable headers

* update test assertion

Author: lilnasy

packages/astro/src/core/request.ts

@@ -70,7 +70,7 @@ export function createRequest({
 			get() {
 				logger.warn(
 					null,
-					`\`Astro.request.headers\` is not available in "static" output mode. To enable header access: set \`output: "server"\` or \`output: "hybrid"\` in your config file.`
+					`\`Astro.request.headers\` is unavailable in "static" output mode, and in prerendered pages within "hybrid" and "server" output modes. If you need access to request headers, make sure that \`output\` is configured as either \`"server"\` or \`output: "hybrid"\` in your config file, and that the page accessing the headers is rendered on-demand.`
 				);
 				return _headers;
 			},

packages/astro/test/static-build.test.js

@@ -186,7 +186,7 @@ describe('Static build', () => {
 	it('warns when accessing headers', async () => {
 		let found = false;
 		for (const log of logs) {
-			if (/`Astro\.request\.headers` is not available in "static" output mode/.test(log.message)) {
+			if (/`Astro\.request\.headers` is unavailable in "static" output mode/.test(log.message)) {
 				found = true;
 			}
 		}