The runners have MinGW installed in 2 locations:
- C:\Program Files\Git\mingw64 uses msvcrt.dll and ucrtbase.dll
- C:\mingw64 uses only (the new) ucrtbase.dll
CMake is using the compiler from C:\mingw64 but at runtime it is still loading the
`libstdc++-6.dll` from the Git-MinGW as it is started from the Git bash.
This causes conflicts with functions compiled into the executable and those used by the runtime.
Most notably the string from `abi::__cxa_demangle` is allocated on a different heap
so freeing it with `free` called from the executable corrupts the heap leading to a SIGSEGV / Exit code 0xc0000374 in the tests.
B2 doesn't suffer from this as it modifies `$PATH` when running each test such that the right libraries are used.
Do it similarly in the GHA-CI config.
Avoid:
> fatal: detected dubious ownership in repository at '/__w/turtle/turtle'
by adding that path to the git `safe.path`.
This is caused by the command(s) running inside the container but the
folder being created outside the container so the owner inside the container is not what is expected by git.
