fix: add gemini key as env var in workflow and make config file optional

.github/workflows/api_pull_request.yml

@@ -56,6 +56,8 @@ jobs:
       - name: Build project
         run: dotnet build ./AltGen.API.Tests/AltGen.API.Tests.csproj --no-restore
       - name: Test project
+        env:
+          Gemini__ApiKey: ${{ secrets.GEMINI_APIKEY }}
         run: dotnet test ./AltGen.API.Tests/AltGen.API.Tests.csproj --filter FullyQualifiedName!~PromptEvaluation
       - name: Upload test coverage report
         uses: actions/upload-artifact@v4

src/AltGen.API.Tests/Fixtures/TestConfiguration.cs

@@ -5,7 +5,7 @@ namespace AltGen.API.Tests.Fixtures;
 public class TestConfiguration
 {
   static IConfiguration Config { get; } = new ConfigurationBuilder()
-    .AddJsonFile("appsettings.Test.json")
+    .AddJsonFile("appsettings.Test.json", optional: true)
     .AddEnvironmentVariables()
     .Build();