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/Certificate/New-CSCertificate.Tests.ps1

@@ -0,0 +1,33 @@
+BeforeAll {
+    $ManifestFile = (Get-Item -Path "./src/*.psd1").FullName
+    Import-Module $ManifestFile -Force
+
+    $PrivateFunctions = (Get-ChildItem -Path "./src/Private/*.ps1" | Where-Object {
+            $_.BaseName -notmatch '.Tests'
+        }
+    ).FullName
+    foreach ( $func in $PrivateFunctions) {
+        . $func
+    }
+}
+
+Describe "New-CSCertificate" {
+    Context "Basic Tests" -Tag 'Unit' {
+        It "Should not throw" {
+            $attribs = @{
+                Country                = 'DE'
+                State                  = 'BW'
+                City                   = 'KA'
+                Organization           = 'IT'
+                OrganizationalUnitName = 'foo'
+                CommonName             = 'MyCert'
+            }
+            $CertAttribs = @{
+                CRTAttribute = New-CSCertAttribute @attribs
+                KeyName      = Join-Path -Path (Get-TempDir) -ChildPath '/foo.key'
+                CertName     = Join-Path -Path (Get-TempDir) -ChildPath '/cert.pfx'
+            }
+            { New-CSCertificate @CertAttribs } | Should -Not -Throw
+        }
+    }
+}