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: #59

src/Store/Get-CredentialStore.Tests.ps1

@@ -0,0 +1,47 @@
+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 "Get-CredentialStore" {
+    Context "Basic logic tests" {
+        It "Read CS without params" {
+            $TestCredentialStore = './resources/cs/CredentialStore.json'
+            $TestPfxCert = './resources/cs/PSCredentialStore.pfx'
+            if (! (Test-Path -Path (Get-DefaultCredentialStorePath)) ) {
+                { New-CredentialStore -Force } | Should -Not -Throw
+            }
+            { Get-CredentialStore } | Should -Not -Throw
+        }
+        It "Read Credential Store with testing data" {
+            $TestCredentialStore = './resources/cs/CredentialStore.json'
+            $TestPfxCert = './resources/cs/PSCredentialStore.pfx'
+            {
+                Use-CSCertificate -Shared -CredentialStore $TestCredentialStore -Path $TestPfxCert
+            } | Should -Not -Throw
+            { Get-CredentialStore -Shared -Path $TestCredentialStore } | Should -Not -Throw
+        }
+        It "Test3: Not existing path should return false" {
+            {
+                Get-CredentialStore -Shared -Path './CredentialStore.json'
+            } | Should -Throw "Could not find the CredentialStore."
+        }
+    }
+    Context "Testing invalid json data" {
+        It "Should throw with invalid CredentialStore" {
+            $BrokenCS = './resources/cs/Broken_CS.json'
+            Write-Verbose -Message ('BrokenCS Path: {0}' -f $BrokenCS) -Verbose
+            {
+                Get-CredentialStore -Path -Shared $BrokenCS
+            } | Should -Throw
+        }
+    }
+}