prepare new release

update miniz_oxide dependency to 0.8.x

update maintenance guide with recent news

Specify a minimum version of the Rust compiler that successfully
builds the crate. This allows us to be aware if the minimal version
increases and to avoid issues such as
#370

The minimum version is a best-effort measured value and is different to
the MSRV which is a support guarantee. The minimum version can be
incremented by a PR in order to pass tests, as long as the MSRV holds.
When the minimum version increases, the next release should be a minor
version, to allow any affected users to pin to a previous minor version.

Check minimal version of Rust that compiles

Remove non-existent build in CI

Return error instead of packing on Z_MEM_ERROR

Since it is possible to for dependencies to bump MSRV in patch release, msrv checking should use the minimal versions supported by flate2.

Users cares deeply about msrv can also pin them to the minimal versions to maintain their current msrv.

This would have also help discover bugs in #424

…test releases.

That way, those compiling with `-Zminimal-versions` have higher chances of it to work.

See GitoxideLabs/gitoxide#1541 for reference.

That way it should compile with minimal versions.

Reason for this is the following:

````
error: package `cc v1.0.98` cannot be built because it requires rustc 1.63 or newer, while the currently active rustc version is 1.56.1
````

Note that the expressed MSRV is still a lower one as it may work for
some people that use different settings and/or configuration.

Fix msrv: Run msrv checks with minimal versions