fix(gitlab): workaround hotlinking protection (406 Not Acceptable)

[andreymart-test]

problem:
#97

reason:
This returns an Error 406, Im guessing due to the hotlinking rules
https://gitlab.com/gitlab-org/gitlab/-/commit/50c11f278d18fe1f3fb12eb595067216bb58ade2

solved:
need to add a mode mode: 'same-origin' in fetch that solves the problem.

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (1945818) 55.07% compared to head (81e327f) 54.93%.

Files	Patch %	Lines
src/_utils.ts	60.00%	2 Missing ⚠️
src/providers.ts	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #123      +/-   ##
==========================================
- Coverage   55.07%   54.93%   -0.15%     
==========================================
  Files           7        7              
  Lines         601      608       +7     
  Branches       46       47       +1     
==========================================
+ Hits          331      334       +3     
- Misses        269      273       +4     
  Partials        1        1              

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[pi0]

Thanks for working on this dear @andreymart-test ❤️

I have made slight changes to only set mode and header for gitlab provider as it seems adding mode breaks other providers like github.