Fix LocalStack AWS client endpoint configuration

- Remove RegionEndpoint from client configs when using ServiceURL
- Use BasicAWSCredentials instead of AnonymousAWSCredentials
- Add ForcePathStyle to SQS config for proper endpoint resolution
- Prevents clients from falling back to real AWS endpoints

Author: NinjaRocks

tests/SourceFlow.Cloud.AWS.Tests/TestHelpers/LocalStackTestFixture.cs

@@ -143,15 +143,18 @@ public async Task InitializeAsync()
         }
 
         // Create AWS clients configured for LocalStack
-        // Use AnonymousAWSCredentials to bypass credential validation in LocalStack
-        var credentials = new Amazon.Runtime.AnonymousAWSCredentials();
+        // Use BasicAWSCredentials with dummy values for LocalStack
+        // AnonymousAWSCredentials can cause issues with endpoint resolution
+        var credentials = new Amazon.Runtime.BasicAWSCredentials("test", "test");
 
         var config = new Amazon.SQS.AmazonSQSConfig
         {
             ServiceURL = LocalStackEndpoint,
             UseHttp = true,
-            RegionEndpoint = _configuration.Region,
-            AuthenticationRegion = _configuration.Region.SystemName
+            // Don't set RegionEndpoint when using ServiceURL - it can override the endpoint
+            AuthenticationRegion = _configuration.Region.SystemName,
+            // Force the use of the custom endpoint
+            ForcePathStyle = true
         };
 
         SqsClient = new AmazonSQSClient(credentials, config);
@@ -160,7 +163,7 @@ public async Task InitializeAsync()
         {
             ServiceURL = LocalStackEndpoint,
             UseHttp = true,
-            RegionEndpoint = _configuration.Region,
+            // Don't set RegionEndpoint when using ServiceURL
             AuthenticationRegion = _configuration.Region.SystemName
         };
 
@@ -170,7 +173,7 @@ public async Task InitializeAsync()
         {
             ServiceURL = LocalStackEndpoint,
             UseHttp = true,
-            RegionEndpoint = _configuration.Region,
+            // Don't set RegionEndpoint when using ServiceURL
             AuthenticationRegion = _configuration.Region.SystemName
         };