Fix static file endpoints after Astro v4 upgrade

Yesterday I upgraded to Astro v4 without any issues, but this morning I noticed that my RSS feed was broken.

I have two static file endpoints that generate a file at build time, one for RSS and the other for a webfinger. Both of these had two issues highlighted after the upgrade:

1. The files did not export a GET function
2. The files did not return a Response or Promise<Response>

The first issue was resolved by capitalizing the previously-valid get function to GET.

The second issue required an update to the @astrojs/rss dependency which now returns a Promise<Response>. The webfinger endpoint is custom, but all I needed to do was wrap my return value with a Response object:

// Before
return { body: JSON.stringify(data, null, 2) };

// After
return new Response(JSON.stringify(data, null, 2));

The webfinger issue is easy to miss (and nonconsequential), but I should have verified that the RSS feed was working before shipping the upgrade. Lessons learned!