Update text and links in announce templates

The links were still pointing to the latest version (instead of stable)
and also took the opportunity to update the text a bit.

scripts/release.patch.rst

@@ -7,9 +7,9 @@ This is a bug-fix release, being a drop-in replacement. To upgrade::
 
   pip install --upgrade pytest
 
-The full changelog is available at https://docs.pytest.org/en/latest/changelog.html.
+The full changelog is available at https://docs.pytest.org/en/stable/changelog.html.
 
-Thanks to all who contributed to this release, among them:
+Thanks to all of the contributors to this release:
 
 {contributors}