Improve URL checks to reduce false-negatives

This commit improves the URL health checking mechanism to reduce false
negatives.

- Treat all 2XX status codes as successful, addressing issues with codes
  like `204`.
- Exclude URLs within Markdown inline code blocks.
- Send the Host header for improved handling of webpages behind proxies.
- Improve formatting and context for output messages.
- Fix the defaulting options for redirects and cookie handling.
- Add URL exclusion support for non-responsive URLs.
- Update the user agent pool to modern browsers and platforms.
- Improve CI/CD workflow to respond to modifications in the
  `test/checks/external-urls` directory, offering immediate feedback on
  potential impacts to the external URL test.
- Add support for randomizing TLS fingerprint to mimic various clients
  better, improving the effectiveness of checks. However, this is not
  fully supported by Node.js's HTTP client; see nodejs/undici#1983 for
  more details.
- Use `AbortSignal` instead of `AbortController` as more modern and
  simpler way to handle timeouts.

tests/checks/external-urls/StatusChecker/UrlStatus.ts

@@ -0,0 +1,19 @@
+import { indentText } from '@tests/shared/Text';
+
+export interface UrlStatus {
+  readonly url: string;
+  readonly error?: string;
+  readonly code?: number;
+}
+
+export function formatUrlStatus(status: UrlStatus): string {
+  return [
+    `URL: ${status.url}`,
+    ...status.code !== undefined ? [
+      `Response code: ${status.code}`,
+    ] : [],
+    ...status.error ? [
+      `Error:\n${indentText(status.error)}`,
+    ] : [],
+  ].join('\n');
+}