fix: run Pester tests only once - #4

Objective

Correct the PimsOS CI workflow so each Unit and Integration campaign runs Pester once and generates its NUnit report during that same execution.

Changes

• keep the existing concurrency protection;
• remove obsolete Tools/** trigger path;
• track Tests/PesterConfiguration.ps1 instead of the old root path;
• generate Unit and Integration NUnit XML directly during their respective Pester runs;
• remove the two redundant Pester report-generation executions.

Validation

• local workflow diff checked with git diff --check;
• exactly 2 Invoke-Pester calls remain;
• no obsolete workflow paths remain.

The branch contains only the CI workflow commit on top of c36f068.