Update PULL_REQUEST_TEMPLATE.md (#1681)

Small typo on the PR template.

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,7 +1,7 @@
 The starting point for contributions should usually be [a discussion](https://github.com/encode/httpx/discussions)
 
 Simple documentation typos may be raised as stand-alone pull requests, but otherwise
-please ensure you've discussed the your proposal prior to issuing a pull request.
+please ensure you've discussed your proposal prior to issuing a pull request.
 
 This will help us direct work appropriately, and ensure that any suggested changes
 have been okayed by the maintainers.