Initial Mbed-TLS 3 support to get the GitHub Actions working again
mingw has upgraded to Mbed-TLS 3.1.0, so all the mingw tests that need
Mbed-TLS currently don't work.
v2: add missing mbedtls/version.h into test/regress_mbedtls.c
v3: suppress #warning "Including compat-2.x.h is deprecated" for mbedtls/compat-2.x.h
