Migrates to Pester5+ tests (#59)

#### 📖 Summary

- update Pester tests to Pester5+ compatiple layout
- switch to dotnet base imaged
  - dotnet binary required for publishung powershell modules (Publish-Module)

#### 📑 Test Plan

> 💡 Select your test plan for the code changes.

- [x] Tested via Drone.io pipeline
- [ ] Custom test
- [ ] No test plan

##### Details / Justification

<!-- Add your test details or justification for missing tests here. -->

#### 📚 Additional Notes

<!-- A place for additional detail notes. -->

Co-authored-by: OCram85 <marco.blessing@googlemail.com>
Reviewed-on: OCram85/PSCredentialStore#59

src/PSModule.Tests.ps1

@@ -1,14 +1,12 @@
 Describe 'Test module meta' {
-    It 'Test manifest file' {
-        $ManifestFile = (Get-Item -Path "./src/*.psd1").FullName
-        Test-ModuleManifest -Path $ManifestFile | Should -Be $true
+    Context 'Default tests' -Tag 'Default' {
+        It 'Test manifest file' {
+            $ManifestFile = (Get-Item -Path "./src/*.psd1").FullName
+            Test-ModuleManifest -Path $ManifestFile | Should -Be $true
+        }
+        It 'Import Module' {
+            $ManifestFile = (Get-Item -Path "./src/*.psd1").FullName
+            { Import-Module $ManifestFile } | Should -Not -Throw
+        }
     }
-    It 'Import Module' {
-        $ManifestFile = (Get-Item -Path "./src/*.psd1").FullName
-        { Import-Module $ManifestFile } | Should -Not -Throw
-    }
-    # Dummy test to force pester error
-    #It 'Force Pester Error' {
-    #    $true | Should -BeFalse
-    #}
 }