chore: fix MSRV build

[gruebel]

This PR

• had to increase the MSRC version to 1.71.1, because of mockall and tokio

[prnam]

There is no need for 1.67.1 rustc build, @gruebel and @beeme1mr? 🤔

[gruebel]

@prnam it always depends, we try to support the lowest possible version, but now 2 dependencies need a higher one, so it seems for me to be a good time to increase the minimum supported version.

[sheepduke]

@prnam it always depends, we try to support the lowest possible version, but now 2 dependencies need a higher one, so it seems for me to be a good time to increase the minimum supported version.

I strongly agree that the versions of the dependencies (compiler version included) needs to be kept up-to-date to prevent the project from decaying.

I do not mind upgrading the compiler version at all...

Good work @gruebel 👍