Incorrect MIME type for .css and .js files breaks rendering of HTML reports

[knedlsepp]

Describe the bug HTML reports are no longer rendered correctly since https://github.com/NixOS/hydra/pull/1240 was merged, as the Content-Type of .css and .js files changed from text/css or application/javascript to text/plain.

Firefox reports:

The stylesheet was not loaded because its MIME type, "text/plain" is not "text/css"

To Reproduce

Visit https://hydra.nixos.org/build/203389362 and click Manual. Or try visiting one of the following:

• https://nixos.org/nixops/manual
• https://nixos.org/hydra/manual

Screenshots

Hydra Server:

• OS and version: e.g. NixOS 22.11.20221229.ad35830
• Version of Hydra: hydra-unstable 2022-10-22
• Version of Nix Hydra is built against: nix-2.11.1
• Version of the Nix daemon: nix-2.11.1

[peacememories]

It seems not only the css and js MIME-types are broken. When trying to view the page on an iPhone, it is instead downloaded, because the content type header looks like this:

content-type: cannot  open  `/nix/store/mp2x9s34n3m2lyd7hk9x15l1sry5qkda-hydra-manual-0.1.20221021.312cb42/share/doc/hydra/index.html'  (No such file or directory); charset=cannot open  `/nix/store/mp2x9s34n3m2lyd7hk9x15l1sry5qkda-hydra-manual-0.1.20221021.312cb42/share/doc/hydra/index.html'  (No such file or directory)

My desktop browser ignores this, but mobile Safari refuses to open the page and instead opens the download dialog.