zlib source code failed to download in VPN (ZScaler)

When running the training in the docker and enabled my VPN (ZSCaler), the download of the source code from sourceforge will fail.

This fails in Ex.16, when cross-building the zlib:
```
zlib/1.2.11: Configuring sources in /home/conan/.conan/data/zlib/1.2.11/_/_/source
ERROR: Error downloading file https://zlib.net/zlib-1.2.11.tar.gz: 'HTTPSConnectionPool(host='zlib.net', port=443): Max retries exceeded with url: /zlib-1.2.11.tar.gz (Caused by SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c:1076)')))'
```
wget will fail too:
```
wget https://downloads.sourceforge.net/project/libpng/zlib/1.2.11/zlib-1.2.11.tar.gz
ERROR: cannot verify downloads.sourceforge.net's certificate, issued by 'CN=Zscaler Intermediate Root CA (zscaler.net) (t)\\ ,OU=Zscaler Inc.,O=Zscaler Inc.,ST=California,C=US':
Unable to locally verify the issuer's authority.
To connect to downloads.sourceforge.net insecurely, use `--no-check-certificate'
```

I have checked without the VPN and it works. Other users worked for them, even if using ZScaler too.

Start with Ex.16, the Docker training environment, and the zlib 1.2.11 source download path. Reproduce the failure with ZScaler enabled and compare it with the working non-VPN case, including the certificate setup shown in the error output. Done means the zlib source downloads successfully in the affected training environment.

Written by the indexing model from the issue text.