templates/release: update OpenSlide Python CI after release

Signed-off-by: Benjamin Gilbert <bgilbert@cs.cmu.edu>

Author: bgilbert

.github/ISSUE_TEMPLATE/release.md

@@ -6,3 +6,4 @@
 - [ ] Verify that CI creates a [GitHub release](https://github.com/openslide/openslide-winbuild/releases/) with artifacts
 - [ ] Update website: `_data/releases.yaml`, maybe `_includes/news.md`
 - [ ] Possibly send mail to -announce and -users
+- [ ] Update `WINBUILD_RELEASE` in [OpenSlide Python CI](https://github.com/openslide/openslide-python/blob/main/.github/workflows/python.yml)