Bump msrv to 1.65

[NobodyXu]

Required for #1137

[NobodyXu]

Unfortunately Debian stable is still on 1.63 https://packages.debian.org/search?keywords=rustc

[ChrisDenton]

What is the actual MSRV policy currently? It's used to be roughly stable - 2. But then this crate languished for awhile so the practical MSRV slipped further through inaction. While I don't think this needs the MSRV to be as aggressive as it used to be, I'm also not sure there's much reason to have Debian LTS as a baseline, It appears they already ship a cc-rs package: https://packages.debian.org/search?suite=default&section=all&arch=any&searchon=names&keywords=librust-cc

[thomcc]

I'd be fine with something like stable-5 (IIRC the libs team agreed that this would be good for libc, so I'm just cribbing from that). I know a lot of people have strong feelings about MSRV, but ancient MSRVs increase maintenance burden and we are low on those resources.

[thomcc]

More concretely, 1.65 is from 2022 so it seems fine to update to that now.