chore(deps): update dependency myst-parser to v5

Author: renovate[bot]

docs/requirements.txt

@@ -2,7 +2,7 @@
 canonical-sphinx==0.6.0
 
 # Extensions previously auto-loaded by canonical-sphinx
-myst-parser==4.0.1
+myst-parser==5.0.0
 sphinx-autobuild==2025.8.25
 sphinx-design==0.7.0
 sphinx-notfound-page==1.1.0