When setting `url.host` on a URL object with no port specified (like is
the case of default port), the resulting URL's port will not change.
Workaround this quirk in the URL standard by explicitely setting port
for the http and https protocols.
Extracted the logic to a function for the purpose of testing. Initially
I wanted to have the function in utils.js, but it turns out esbuild can
not treeshake the unused functions which would result in the
webcomponents chunk having all 2kB utils.js inlined, so it seemed not
worth.
Fixes: https://github.com/go-gitea/gitea/issues/29084
