detect/transform: fix leak in xor transform parse

[catenacyber]

Link to ticket: https://redmine.openinfosecfoundation.org/issues/
https://redmine.openinfosecfoundation.org/issues/7229 follow up

Describe changes:

• detect/transform: fix leak in xor transform parse

Fixes: 8984bc6 ("transforms: move xor to rust")

[catenacyber]

I wonder why oss-fuzz did not catch it

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 49.78%. Comparing base (13841c0) to head (c26cb9a).

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #12147   +/-   ##
=======================================
  Coverage   49.77%   49.78%           
=======================================
  Files         909      909           
  Lines      257884   257887    +3     
=======================================
+ Hits       128367   128391   +24     
+ Misses     129517   129496   -21     

Flag	Coverage Δ
fuzzcorpus	60.93% <100.00%> (-0.01%)	⬇️
livemode	19.43% <0.00%> (-0.01%)	⬇️
pcap	44.38% <0.00%> (-0.02%)	⬇️
suricata-verify	62.69% <0.00%> (+<0.01%)	⬆️
unittests	8.98% <0.00%> (-0.01%)	⬇️

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[suricata-qa]

Information: QA ran without warnings.

Pipeline 23514