Docker build fails due to gcc being missing

[Yard1]

Since yesterday (8th of December) the Action fails as it tries to build cryptography with gcc, which is missing from the python3.8:slim image.

    running build_ext
    generating cffi module 'build/temp.linux-x86_64-3.8/_padding.c'
    creating build/temp.linux-x86_64-3.8
    generating cffi module 'build/temp.linux-x86_64-3.8/_openssl.c'
    building '_openssl' extension
    creating build/temp.linux-x86_64-3.8/build
    creating build/temp.linux-x86_64-3.8/build/temp.linux-x86_64-3.8
    gcc -pthread -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -fPIC -I/usr/local/include/python3.8 -c build/temp.linux-x86_64-3.8/_openssl.c -o build/temp.linux-x86_64-3.8/build/temp.linux-x86_64-3.8/_openssl.o -Wconversion -Wno-error=sign-conversion
    unable to execute 'gcc': No such file or directory
    
        =============================DEBUG ASSISTANCE=============================
        If you are seeing a compilation error please try the following steps to
        successfully install cryptography:
        1) Upgrade to the latest pip and try again. This will fix errors for most
           users. See: pip.pypa.io/en/stable/installing/#upgrading-pip
        2) Read cryptography.io/en/latest/installation.html for specific
           instructions for your platform.
        3) Check our frequently asked questions for more information:
           cryptography.io/en/latest/faq.html
        =============================DEBUG ASSISTANCE=============================
    
    error: command 'gcc' failed with exit status 1
    ----------------------------------------
    ERROR: Failed building wheel for cryptography
  Failed to build cryptography
  ERROR: Could not build wheels for cryptography which use PEP 517 and cannot be installed directly
  The command '/bin/sh -c pip install --upgrade --no-cache-dir twine' returned a non-zero code: 1

[Yard1]

Scratch that, it worked after rerunning twice. Quite odd, though.

[webknjaz]

Sounds like a duplicate of #50. See the explanation there.