docs: remove unintended characters in subdomain section in csrf page

[yonbh]

Small corrections to subdomain section in csrf debug page.

Related issue(s)

Checklist

• I have read the contributing guidelines.
• I have referenced an issue containing the design document if my change
  introduces a new feature.
• I am following the
  contributing code guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security. vulnerability, I
  confirm that I got green light (please contact
  [email protected]) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further Comments

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #1897 (9fec612) into master (1e794fe) will decrease coverage by 0.06%.
The diff coverage is n/a.

❗ Current head 9fec612 differs from pull request most recent head f907c82. Consider uploading reports for the commit f907c82 to get more accurate results

@@            Coverage Diff             @@
##           master    #1897      +/-   ##
==========================================
- Coverage   75.13%   75.07%   -0.07%     
==========================================
  Files         292      292              
  Lines       15127    15125       -2     
==========================================
- Hits        11366    11355      -11     
- Misses       2950     2958       +8     
- Partials      811      812       +1     

Impacted Files	Coverage Δ
cmd/courier/watch.go	60.34% <0.00%> (-12.07%)	⬇️
internal/testhelpers/e2e_server.go	87.82% <0.00%> (-1.74%)	⬇️
persistence/sql/persister_recovery.go	79.54% <0.00%> (-0.46%)	⬇️
selfservice/strategy/link/token_recovery.go	100.00% <0.00%> (ø)
selfservice/strategy/link/test/persistence.go	100.00% <0.00%> (ø)
selfservice/strategy/link/strategy_recovery.go	65.08% <0.00%> (+0.92%)	⬆️

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[aeneasr]

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