Fix URL for old repo in PR template

Co-authored-by: Tom Bland <t.bland@imperial.ac.uk>

Author: alexdewar

.github/PULL_REQUEST_TEMPLATE.md

@@ -9,7 +9,7 @@ Fixes # (issue)
 ## Type of change
 
 Please add a line in the relevant section of
-[CHANGELOG.md](https://github.com/EnergySystemsModellingLab/StarMuse/blob/development/CHANGELOG.md) to
+[CHANGELOG.md](https://github.com/EnergySystemsModellingLab/MUSE_OS/blob/development/CHANGELOG.md) to
 document the change (include PR #) - note reverse order of PR #s.
 
 - [ ] New feature (non-breaking change which adds functionality)