DOCSP-13625 fix formatting on $expr behavior section

Author: andf-mongodb

source/reference/operator/query/expr.txt

@@ -36,12 +36,12 @@ Behavior
 - :query:`$expr` can build query expressions that compare fields 
   from the same document in a :pipeline:`$match` stage.
 
-   - If the :pipeline:`$match` stage is part of a :pipeline:`$lookup`
-     stage, :query:`$expr` can compare fields using ``let`` variables.
-     See :ref:`lookup-multiple-joins` for an example. 
+  - If the :pipeline:`$match` stage is part of a :pipeline:`$lookup`
+    stage, :query:`$expr` can compare fields using ``let`` variables.
+    See :ref:`lookup-multiple-joins` for an example. 
 
-   - :query:`$expr` only uses indexes on the ``from`` collection for
-     equality matches in a :pipeline:`$match` stage.
+  - :query:`$expr` only uses indexes on the ``from`` collection for
+    equality matches in a :pipeline:`$match` stage.
 
 - :query:`$expr` does not support
   :ref:`multikey indexes <index-type-multikey>`.