Fix: ensure upgrade message shows actual installed version

[coder-aditi]

Fix #13434

Previously, when upgrading pip, the output message showed the old version number instead of the new one. This fix makes sure that the success message shows the correct installed version, giving clear feedback during pip upgrades.

[notatallshaw]

Thanks for the PR, please be aware it may take some time to review as pip maintainer time is very limited.

Please let us know if you have any issues fixing the CI issues, you should be able to pre-commit or nox linting locally to find and fix issues: https://pip.pypa.io/en/stable/development/getting-started/#running-linters

[ichard26]

I'm willing to bet that the pip install summary contains the wrong version because there are multiple installations of the same package at once. Either the old version was partially overwritten by the new version or the old version was left dangling due to other reasons. While pip can't warn on duplicate installations in general as shadowing is a valid use case, if there are multiple installations in the same import directory (site-packages or whatever), that would be worth warning about.

In other words, I don't think this is the right approach to fix the issue. We should warn about the underlying issue causing the wrong version to be emitted.