DEV: Ensure Ember CLI sourcemaps are uploaded to S3 (#15893)

Ember CLI gives sourcemaps their own digest. Our `s3.rake` logic assumes that the digest portion of sourcemap filenames remains the same.

The Ember CLI sourcemaps are included in the manifest file, so we can ensure they are uploaded by letting them past the MiniMime check.

Followup to abefb1beff

lib/tasks/s3.rake

@@ -59,9 +59,9 @@ def assets
     fullpath = (Rails.root + "public/assets/#{path}").to_s
 
     # Ignore files we can't find the mime type of, like yarn.lock
-    if mime = MiniMime.lookup_by_filename(fullpath)
-      content_type = mime.content_type
-
+    content_type = MiniMime.lookup_by_filename(fullpath)&.content_type
+    content_type ||= "application/json" if fullpath.end_with?(".map")
+    if content_type
       asset_path = "assets/#{path}"
       results << [fullpath, asset_path, content_type]