ci: deadlink checker ignores https://docs.buf.build/

[seeflood]

Signed-off-by: seeflood [email protected]

What this PR does:
Let the deadlink checker ignores https://docs.buf.build/

Which issue(s) this PR fixes:

Fixes the CI error in #736

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov]

Codecov Report

Merging #737 (91d74c2) into main (0b2d62f) will not change coverage.
The diff coverage is n/a.

❗ Current head 91d74c2 differs from pull request most recent head d022330. Consider uploading reports for the commit d022330 to get more accurate results

@@           Coverage Diff           @@
##             main     #737   +/-   ##
=======================================
  Coverage   60.60%   60.60%           
=======================================
  Files         133      133           
  Lines        8318     8318           
=======================================
  Hits         5041     5041           
  Misses       2700     2700           
  Partials      577      577           

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