fix(security): mitigate potential ReDoS in deprecation link regex (6.x)

[RinZ27]

The deprecation link regex in 6.x is still using a loose pattern that allows for excessive backtracking. Swapping it for the more restrictive logic used in current versions to prevent potential perf hits under load.

[octokit]

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[RinZ27]

Ping on this. It brings the more restrictive deprecation link regex from current versions back to the 6.x branch to mitigate potential ReDoS/backtracking issues. Mind taking a look? Thanks!

[RinZ27]

I decided to update the title to better reflect that this is a security-related backport. This change brings the more restrictive regex logic from current versions into the 6.x branch, specifically to mitigate potential ReDoS issues that I noticed in the older pattern. Since this aligns 6.x with the security improvements already present in newer releases, I'd appreciate it if someone could take a quick look.