Fix Docker build by pinning z3-solver and Python 3.9 pip bootstrap

[eugenioclrc]

Worker was not building as expected, it showed this error:

docker build -t whitehat-machine .
[+] Building 346.6s (28/43)                                                                                                                                            docker:desktop-linux
 => [internal] load build definition from Dockerfile                                                                                                                                   0.0s
 => => transferring dockerfile: 8.20kB                                                                                                                                                 0.0s
 => resolve image config for docker-image://docker.io/docker/dockerfile:1.3                                                                                                            5.9s
 => docker-image://docker.io/docker/dockerfile:1.3@sha256:42399d4635eddd7a9b8a24be879d2f9a930d0ed040a61324cfdf59ef1357b3b2                                                             0.7s
 => => resolve docker.io/docker/dockerfile:1.3@sha256:42399d4635eddd7a9b8a24be879d2f9a930d0ed040a61324cfdf59ef1357b3b2                                                                 0.0s
 => => sha256:56d51bb3d5ad743c8b4b66783cb387af72e1cc4de40cb0d60dd76b4e1315a9c9 528B / 528B                                                                                             0.0s
 => => sha256:09309628c1131db14cdf692fc549798533eef7fbea50735a141bb7383ab81c92 1.21kB / 1.21kB                                                                                         0.0s
........
 => [audit-toolbox 15/32] RUN python3.9 -m pip install --no-cache-dir     solc-select     slither-analyzer pandocfilters pygments PyGithub     halmos &&     git clone https://githu  27.7s
 => [audit-toolbox 16/32] RUN git clone https://github.com/tomlion/vim-solidity.git ~/.vim/pack/plugins/start/vim-solidity                                                             1.1s
 => ERROR [audit-toolbox 17/32] RUN solc-select install 0.8.21  &&     solc-select use 0.8.21                                                                                          0.1s
------
 > [audit-toolbox 17/32] RUN solc-select install 0.8.21  &&     solc-select use 0.8.21:
0.106 /bin/sh: 1: solc-select: not found
------
ERROR: failed to build: failed to solve: process "/bin/sh -c solc-select install 0.8.21  &&     solc-select use 0.8.21" did not complete successfully: exit code: 127

View build details: docker-desktop://dashboard/build/desktop-linux/desktop-linux/k7qixsqs06ffjomas9jd4tb1g