ci: use python virtual env in self-hosted workflows

Since this morning, our QA Integration Tests started failing during installation of `rpc-tests` dependencies. This command:
```shell
pip3 install -r requirements.txt
```
triggers the following error:
```
error: externally-managed-environment

× This environment is externally managed
╰─> To install Python packages system-wide, try apt install
python3-xyz, where xyz is the package you are trying to
install.

If you wish to install a non-Debian-packaged Python package,
create a virtual environment using python3 -m venv path/to/venv.
Then use path/to/venv/bin/python and path/to/venv/bin/pip. Make
sure you have python3-full installed.

If you wish to install a non-Debian packaged Python application,
it may be easiest to use pipx install xyz, which will manage a
virtual environment for you. Make sure you have pipx installed.

See /usr/share/doc/python3.12/README.venv for more information.

note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.
hint: See PEP 668 for the detailed specification.
```

See [here](https://github.com/erigontech/silkworm/actions/runs/11948569211/job/33308220992) for details.

We added the `--break-system-packages` option to temporarily fix the problem, but a solution with virtual environment is highly preferable.