Fix some headers that were incorrectly comments

tutorials/shaders/screen-reading_shaders.rst

@@ -108,7 +108,7 @@ With correct back-buffer copying, the two spheres blend correctly:
 
 .. image:: img/texscreen_demo2.png
 
-.. warning:
+.. warning::
 
     In 3D, materials that use ``hint_screen_texture`` are considered transparent themselves and
     will not appear in the resulting screen texture of other materials.

tutorials/xr/index.rst

@@ -25,7 +25,7 @@ Advanced topics
    openxr_hand_tracking
    openxr_passthrough
 
-.. note:
-   
+.. note::
+
    Documentation for XR in Godot 4.0 XR is still a work in progress.
    Please check back in the future.