[github] Fixed the link anchor to CONTRIBUTING.md (anza-xyz#131)

Anchor "#pull-requests" does not exist anymore in CONTRIBUTING.md.
Changed the link in the PR Template  to point to "#developer-workflow"
which does exists, and contains basically the same stuff
"#pull-requests" used to contain.

.github/PULL_REQUEST_TEMPLATE.md

@@ -8,7 +8,7 @@ The project is undergoing daily changes. Pull Requests will be reviewed and resp
 
 (Write your motivation for proposed changes here.)
 
-### Have you read the [Contributing Guidelines on pull requests](https://github.com/move-language/move/blob/main/CONTRIBUTING.md#pull-requests)?
+### Have you read the [Contributing Guidelines on pull requests](https://github.com/move-language/move/blob/main/CONTRIBUTING.md#developer-workflow)?
 
 (Write your answer here.)