Fix typo in doc fail2ban-setup.md

[h00000000]

This fixes a 1 character typo in fail2ban-setup.md

[codecov-io]

Codecov Report

Merging #8914 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #8914      +/-   ##
==========================================
+ Coverage    41.3%   41.31%   +<.01%     
==========================================
  Files         545      545              
  Lines       70368    70368              
==========================================
+ Hits        29068    29075       +7     
+ Misses      37601    37594       -7     
  Partials     3699     3699

Impacted Files	Coverage Δ
models/unit.go	62.16% <0%> (-5.41%)	⬇️
models/repo_list.go	73.3% <0%> (-0.98%)	⬇️
routers/repo/view.go	37.71% <0%> (-0.88%)	⬇️
models/error.go	33.26% <0%> (+0.59%)	⬆️
models/repo_indexer.go	68.36% <0%> (+1.81%)	⬆️
models/pull_list.go	59.85% <0%> (+2.11%)	⬆️
modules/indexer/indexer.go	55.26% <0%> (+10.52%)	⬆️

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[techknowlogick]

ping LG-TM

[techknowlogick]

@huebnerf thanks for PR :)