Merge pull request #618 from scipp/dependabot/pip/requirements/plopp-25.4.0

Bump plopp from 25.3.0 to 25.4.0 in /requirements

Author: jl-wynen

requirements/base.txt

@@ -50,7 +50,7 @@ packaging==24.2
     #   matplotlib
 pillow==11.1.0
     # via matplotlib
-plopp==25.3.0
+plopp==25.4.0
     # via -r base.in
 pydantic==2.10.6
     # via -r base.in