fix: set async: false for tests that manipulate environment variables

Tests that modify global state like environment variables must run
synchronously to prevent race conditions. Fixed:
- groq_test.exs: Was missing async option (defaulted to true)
- ex_llm_pipeline_api_test.exs: Was explicitly set to async: true

This prevents tests from interfering with each other's API keys.

Author: azmaveth

test/ex_llm/providers/groq_test.exs

@@ -1,5 +1,5 @@
 defmodule ExLLM.Providers.GroqTest do
-  use ExUnit.Case
+  use ExUnit.Case, async: false
   alias ExLLM.Providers.Groq
   alias ExLLM.Testing.ConfigProviderHelper
 

test/ex_llm_pipeline_api_test.exs

@@ -1,5 +1,5 @@
 defmodule ExLLM.PipelineAPITest do
-  use ExUnit.Case, async: true
+  use ExUnit.Case, async: false
 
   alias ExLLM.Pipeline.Request
   alias ExLLM.Plugs