Fix documentation errors (#11536)

In trialing an upgrade of sphinx-autoapi to 1.5.1 (it has other
problem with metaclasses right now, so we cant use it just yet) I
noticed these cases of warnings that would become errors if we upgraded.

airflow/operators/python.py

@@ -564,10 +564,18 @@ def get_current_context() -> Dict[str, Any]:
     Obtain the execution context for the currently executing operator without
     altering user method's signature.
     This is the simplest method of retrieving the execution context dictionary.
-    ** Old style:
+
+    **Old style:**
+
+    .. code:: python
+
         def my_task(**context):
             ti = context["ti"]
-    ** New style:
+
+    **New style:**
+
+    .. code:: python
+
         from airflow.task.context import get_current_context
         def my_task():
             context = get_current_context()

airflow/secrets/local_filesystem.py

@@ -48,7 +48,7 @@ def get_connection_parameter_names() -> Set[str]:
 
 def _parse_env_file(file_path: str) -> Tuple[Dict[str, List[str]], List[FileSyntaxError]]:
     """
-    Parse a file in the ``.env '' format.
+    Parse a file in the ``.env`` format.
 
     .. code-block:: text