gh-135490: Add warning about arguments that conflict with pdb

[SnoopJ]

Closes #135490.

This changeset adds a warning to the pdb docs explaining that target program arguments that overlap with pdb arguments must be separated from the rest of the command line by -- to prevent confusion on the part of argparse.

Should only be merged if a fix for that issue does not materialize, although the pdb target.py -- -m XYZ case is likely to apply even if there is a fix for the the repeated -m case.

Screenshot

• Issue: pdb consumes arguments greedily #135490

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📚 Documentation preview 📚: https://cpython-previews--135520.org.readthedocs.build/

[ZeroIntensity]

I think this should be a note, not a warning. Warnings are typically reserved for security problems and things along those lines.

[gaogaotiantian]

I agree that this should be be a warning. However, let's hold it off until I figure out what we should do about the actual behavior, because -m might just work and we don't need to use it as an example to confuse users. -p does not start a script so it won't take any extra arguments and everything might just magically work.