Move Testing section to above instructions in PR template. (#37091)

Makes it harder to just "highlight to end and delete" and miss the Testing
section entirely.

Author: bzbarsky-apple

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,18 +1,19 @@
+
+#### Testing
+
 > !!!!!!!!!! Please delete the instructions below and replace with PR
-> description
+> description above.
 >
 > If you have an issue number, please use a syntax of `Fixes #12345` and a brief
 > change description
 >
 > If you do not have an issue number, please have a good description of the
 > problem and the fix. Help the reviewer understand what to expect.
 >
-> Complete/append to the `### Testing` section below, to describe how testing
+> Complete/append to the `### Testing` section above, to describe how testing
 > was done. See
 > <https://github.com/project-chip/connectedhomeip/blob/master/CONTRIBUTING.md#pull-requests>
 >
 > Make sure you delete these instructions (to prove you have read them).
 >
 > !!!!!!!!!! Instructions end
-
-#### Testing