Update secure-coding-training.html.md - add survey link to get feedback

Why is this change being made?

Continue to get feedback on the training as new GitLabbers take it.

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what