userguide: fix spelling of `security_result` EVE field

[satta]

This ensures that the correct spelling of the security_result EVE field for RFB (as opposed to security-result) is also reflected in the documentation.

• [X] I have read the contributing guide lines at https://docs.suricata.io/en/latest/devguide/contributing/contribution-process.html
• [X] I have signed the Open Information Security Foundation contribution agreement at https://suricata.io/about/contribution-agreement/ (note: this is only required once)
• [X] I have updated the user guide (in doc/userguide/) to reflect the changes made (if applicable)
• [X] I have created a ticket at https://redmine.openinfosecfoundation.org/projects/suricata/issues (if applicable)

Link to ticket: https://redmine.openinfosecfoundation.org/issues/7210

Describe changes:

• Change string security_result to security_result in EVE format documentation to match the actual behaviour.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 82.62%. Comparing base (304271e) to head (b4fc1b8). Report is 50 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #11628   +/-   ##
=======================================
  Coverage   82.61%   82.62%           
=======================================
  Files         919      919           
  Lines      248997   248997           
=======================================
+ Hits       205717   205730   +13     
+ Misses      43280    43267   -13     

Flag	Coverage Δ
fuzzcorpus	60.88% <ø> (ø)
livemode	18.82% <ø> (+0.16%)	:arrow_up:
pcap	44.16% <ø> (+0.01%)	:arrow_up:
suricata-verify	61.89% <ø> (-0.01%)	:arrow_down:
unittests	59.00% <ø> (-0.01%)	:arrow_down:

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[victorjulien]

Merged in #11689, thanks!