Added fixture to test parsing of hash keys ending with a space and #
[Yaml] fixed mapping keys containing a quoted #
bug #11788 [Yaml] fixed mapping keys containing a quoted # (hvt, fabpot)

This PR was merged into the 2.3 branch.

Discussion
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[Yaml] fixed mapping keys containing a quoted #

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11700, #11723
| License       | MIT
| Doc PR        | n/a

Commits
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110f999 [Yaml] fixed mapping keys containing a quoted #
8ba3b28 Added fixture to test parsing of hash keys ending with a space and #
[Security] Use hash_equals for constant-time string comparison