Fix #493 import-module loses previously stored configuration

[mnieto]

PR Summary

When the module is configured with Set-VSTeamAccount -Level user, the configuration is stored in env variables and then recovered next time while import-module vsteam The problem was introduced in commit 0528c76 (#467 closed in #480)

PR Checklist

Note: First 2 checks don't apply because the changes are in the vsteam.psm1 file

• [ ] Write Help
• [ ] Write Unit Test
• [x] Update CHANGELOG.md

[mnieto]

Cancelling PR because the update in the windows-lastest in Github actions forces to update from netcore 3.1 first