Describe the bug

When using the pipx install command with pip arguments -c or --constraint, using a relative path, we encounter an error stating that the file does not exist, even though it does.

How to reproduce

pipx install --pip-args=--constraint=some_constraint_file.txt some_package_inside_constraint_file

Expected behavior

The package should be installed successfully.

I have already identified that this issue occurs following the changes introduced in PR #1237.

Is it necessary to run the commands in a different directory?

If so, I have already begun drafting a solution for this issue.
My approach involves checking for -c and --constraint flags and replacing relative paths with absolute paths before calling the subprocess.

Do you think this proposed solution is appropriate? If there is a simpler way to resolve this issue, please advise.

Thank you very much for this package!