Update dependencies + move to sqlx-oldapi for now

[icewind1991]

sqlx 0.7 still has some issues which are blocking for us (launchbadge/sqlx#2975) so instead this moves to sqlx-oldapi for now which is a fork of 0.6 with some dependency updates.

Fixes #354

[max-nextcloud]

https://github.com/nextcloud/notify_push/actions/runs/7613758006/job/20734418222?pr=383 looks like rustc is too old:

cargo check $cargo_release -j "$NIX_BUILD_CORES" --message-format=$cargo_message_format
error: package `clap_lex v0.6.0` cannot be built because it requires rustc 1.70.0 or newer, while the currently active rustc version is 1.69.0
Either upgrade to rustc 1.70.0 or newer, or use
cargo update -p clap_lex@0.6.0 --precise ver
where `ver` is the latest version of `clap_lex` supporting rustc 1.69.0
[naersk] cargo returned with exit code 101, exiting

I was able to fix a similar failure by using nix 23.11 instead here: 8d47bc8

[max-nextcloud]

That seems like a good approach to be able to update the dependencies fast. First pass over the code changes looks good as well. Did not test locally though.

[max-nextcloud]

@icewind1991 I ran the tests and clippy locally again and everything is green. So good to go from my side. Anything else needed?