Merge pull request #674 from scipp/dependabot/pip/requirements/plopp-26.2.1

Bump plopp from 25.11.0 to 26.2.1 in /requirements

Author: jl-wynen

requirements/base.txt

@@ -49,7 +49,7 @@ packaging==25.0
     #   matplotlib
 pillow==11.3.0
     # via matplotlib
-plopp==25.11.0
+plopp==26.2.1
     # via -r base.in
 pydantic==2.11.7
     # via -r base.in