Unpin dependencies after bumping MSRV beyond 1.65

[toidiu]

Problem:

• One of our dependencies of dependencies (regex) broke MSRV (requires 1.65) in >v1.9.6. To work around this, we have pinned this dependency to =1.9.6.
• s2n-tls-hyper -> hyper -> h2 -> indexmap -> hashbrown =0.15.0 addressed in chore: move hyper to a newer MSRV #4983

Solution:

This should be reverted after bumping MSRV.

[dougch]

#4971