Mergeable is disabled because it was requiring
that PR title follows conventional commit notation
even when PR consisted of multiple commits
and was not planned to be squash merged.
With Python 3.7 asynchronous tests randomly fail
with "RuntimeError: Event loop is closed" during shutdown.
Backtrace of the error includes `SafeChildWatcher` calls.
Python 3.8 has replaced `SafeChildWatcher`
with a new `ThreadedChildWatcher` by default [1]
as a bugfix for
"asyncio.create_subprocess_exec() only works with main event loop" bug [2].
Python 3.7 scheduled end of life is 2023-06-27
according to <https://devguide.python.org/versions/>.
[1] https://github.com/python/cpython/pull/14344
[2] https://bugs.python.org/issue35621
With this, all the builds happen in parallel in 3-6 minutes,
and then python tests run for 8-9 minutes.
Before, it was 6-17 minutes for compilation,
then 19-31 minutes for python tests.
Compilation of the library and test binary was not parallelized,
and then python tests included async python tests
and deltachat-rpc-server binary compilation.
Now, deltachat-rpc-server compilation,
Rust testing and async python tests are separate jobs.
This way if flaky python tests fail,
it is possible to rerun them without having to rerun library compilation.
Python test jobs will redownload already built library artifact
and compile the bindings against it.
cargo-zigbuild is replaced with a simple zig-cc wrapper.
cargo-zigbuild still tries to use i386-linux-musl triple,
while in zig 0.11 x86-linux-musl should be used [1].
This also gives us more control over compilation flags used
and prevents changes due to cargo-zigbuild upgrades,
as its version was not pinned.
[1] Merged PR "all: rename i386 to x86 "
<https://github.com/ziglang/zig/pull/13101>
