chore(ci): pin proptest to 1.8.0 on 1.75.0 MSRV

[oleonardolima]

Description

The proptest dependency is used in bdk_chain, it's already pinned to 1.2.0 on 1.63.0 MSRV, and wasn't a problem on the 1.75.0 MSRV. Recently, it also released a new version, bumping their MSRV, on proptest 1.9.0.

It adds a new step to pin it to 1.8.0 on the 1.75.0 MSRV CI step.

edit: I also had to update the pinned version webpki-roots@1.0.4 and socke2@0.6.1.

Notes to the reviewers

It only applies to release/chain-0.23.x branch; the master is already on 1.85.0 MSRV, which is not affected.

Changelog notice

### Changed
- deps: pin `proptest` to `1.8.0` on `1.75.0` MSRV
# all the pinned dependencies below affect only the `1.63.0` MSRV
- deps: pin `openssl` to `0.10.73`
- deps: pin `openssl-sys` to `0.9.109`
- deps: pin `syn` to `2.0.106`
- deps: pin `quote` to `1.0.41`
- deps: pin `socke2@0.6.1` instead of `0.6.0`
- deps: pin `webpki-roots@1.0.4` instead of `1.0.3`

Checklists

All Submissions:

• I followed the contribution guidelines

[oleonardolima]

I wasn't expecting all these dependencies needing to be pinned for the 1.63.0 MSRV, but the openssl crate did a recent release that bumped their MSRV to 1.70.0, see: https://github.com/rust-openssl/rust-openssl/releases/tag/openssl-v0.10.74

Also, let me know if you think all squashed down to a single commit would be better, I just need this to move forward with #2027.

[ValuedMammal]

ACK 62ce876 No need to squash IMO.

[luisschwab]

ACK 62ce876