fix: incorrectly set cookie's expires value in login.js

[Promix953]

When writing a cookie using document.cookie, the expires value should use the UTCString format.

https://developer.mozilla.org/en-US/docs/Web/API/Document/cookie#write_a_new_cookie

If expires is set incorrectly, the cookie will expire at the end of session and thumbnail will fail to load.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 34.64%. Comparing base (c58c355) to head (f0c9539).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1049   +/-   ##
=======================================
  Coverage   34.64%   34.64%           
=======================================
  Files          61       61           
  Lines        5499     5499           
=======================================
  Hits         1905     1905           
  Misses       3359     3359           
  Partials      235      235           

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[fmartingr]

Hey @Promix953, thank you for taking your time and fixing this issue. Right now it looks good but later on I'm going to provide the ISO directly on the login/refresh APIs to keep that kind of logic out of the frontend. Thank you!