Delete GitLab webhooks with partial URL match

[pat-s]

fix #4248

• Ensure to process all matching webhooks and don't exit after the first one
• Use partial string match as webURL != hook.URL (the latter always has the api/token suffix, the former doesn't)

Tested on gitlab.com.

[codecov]

Codecov Report

Attention: Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.

Project coverage is 26.51%. Comparing base (ddd55ee) to head (cf8d299).
Report is 28 commits behind head on main.

Files with missing lines	Patch %	Lines
server/forge/gitlab/gitlab.go	57.14%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4259      +/-   ##
==========================================
+ Coverage   26.47%   26.51%   +0.04%     
==========================================
  Files         376      377       +1     
  Lines       27465    27447      -18     
==========================================
+ Hits         7270     7278       +8     
+ Misses      19530    19504      -26     
  Partials      665      665              

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[6543]

server/forge/gitlab/gitlab.go:544:2: ineffectual assignment to hookID (ineffassign)
	hookID := -1
	^

[woodpecker-bot]

Tearing down https://woodpecker-ci-woodpecker-pr-4259.surge.sh