Fix link to coaching course

Why is this change being made?

In the Create stage EM training resources handbook page, there is a link to Improve Your Coaching Skills as a Manager under the Coaching section. The current link goes to the mentoring page in the handbook, which I believe is incorrect. Since that mentoring page is already linked just below on that page, and since Improve Your Coaching Skills as a Manager is the name of a LinkedIn Learning course, I updated this link to point to LinkedIn.

Author Checklist

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
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