Fix langchain-ai#3365 + test

Changed regex to cover new line before action serious.

regex101: https://regex101.com/r/CXl1kB/1

tests/unit_tests/agents/test_mrkl.py

@@ -50,6 +50,24 @@ def test_get_action_and_input_newline() -> None:
     assert action_input == "```\nimport unittest\n\nunittest.main()\n```"
 
 
+def test_get_action_and_input_newline_after_keyword() -> None:
+    """Test getting an action and action input from the text
+    when there is a new line before the action (after the keywords "Action:" and "Action Input:") """
+    llm_output = """
+    I can use the `ls` command to list the contents of the directory and `grep` to search for the specific file.
+
+    Action:
+    Terminal
+
+    Action Input:
+    ls -l ~/.bashrc.d/
+    """
+
+    action, action_input = get_action_and_input(llm_output)
+    assert action == "Terminal"
+    assert action_input == "ls -l ~/.bashrc.d/\n"
+
+
 def test_get_final_answer() -> None:
     """Test getting final answer."""
     llm_output = (