Fix healthcheck commands

[evroon]

--spider turns the request into a HEAD request, which we don't support in the backend. So we replace that option by piping to /dev/null instead.

[cloudflare-workers-and-pages]

Deploying bracket-frontend with    Cloudflare Pages

Latest commit:	727ccac
Status:	✅  Deploy successful!
Preview URL:	https://df71e34b.bracket-abd.pages.dev
Branch Preview URL:	https://fix-healthcheck-commands.bracket-abd.pages.dev

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.94%. Comparing base (924e668) to head (727ccac).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1432   +/-   ##
=======================================
  Coverage   94.94%   94.94%           
=======================================
  Files         118      118           
  Lines        4335     4335           
=======================================
  Hits         4116     4116           
  Misses        219      219           

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