Disable some unicode fstring tests for the debugging (f"{...=}") feature since unicode strings come out as "u'...'" in Py2.

Closes https://github.com/cython/cython/issues/3796

Fixes https://github.com/cython/cython/issues/3954

The problem seems to be that __Pyx_CallUnboundCMethod0 optimizes the call incorrectly. This patch avoids it getting sent to that mechanism.

Correct the return type of the ..._GET_TZINFO() macros (which return a borrowed reference) and add corresponding properties so people don't have to use them.

https://foss.heptapod.net/pypy/pypy/-/issues/3404

Let a tracing test run slower to prevent div-by-zero crashes in line_profiler due to measured zero runtime.

Reconfigure ccache and add the backend (C/C++) to the cache key to distinguish between the compiler jobs.

Make sure that test failures are easy to find in the logs by putting all information into the assertion.

Difficult to say which is best, but something around 7-9 apparently.
Accumulated C/C++ compile times only ever go up with increasing shard count (tried 5, 7, 8, 9, 12) but the total test time is lowest at 7-9, depending on the specific run. So, let's waste less cycles overall.

Disable "pycontextvar" test in PyPy which (as of 7.3.4) seems to lack the C-API support for context variables.

Also fixes the control flow analysis for loop variable assignments in this case.
Closes https://github.com/cython/cython/issues/3787

Make a test cleaner for what it should test. We do not care whether (Py2) 'str' works as long as unicode strings work.

Resolve a C compiler warning in the fallback code for PyContextVar_Get() due to an invalid conditional expression that was mixing a void command with a pointer value.