docs: ✏️ refine learning objectives section (#98)

## Description

This PR refines the learning objectives session in the lesson template
by:
- Changing the sections of bold text slightly, so it's more aligned
between the overall learning outcome and the session objective
- Rephrasing the introductory sentence to the overall learning outcome
to directly refer to the learner (I thought that could make the learner
feel more "included"/"engaged")

<!-- Please delete as appropriate: -->
This PR needs a quick review.

## Checklist

- [X] Ran spell-check
- [X] Formatted Markdown

sessions/lesson.qmd

@@ -4,11 +4,11 @@
 
 ## Learning objectives
 
-The **overall learning** outcome of this session is to:
+This session’s **overall learning outcome** is to enable you to:
 
 1.  
 
-Specific **objectives** are to:
+**Specific objectives** are to:
 
 1.  
 
@@ -26,4 +26,4 @@ TODO: Reading text
 
 ## Summary
 
--   TODO: List of summary items
+-   TODO: List of summary items