vim-patch:9.1.0237: filetype: mplstyle files are not recognized

Problem:  filetype: mplstyle files are not recognized
Solution: Detect '*.mplstyle' files as yaml (Wu, Zhenyu)

closes: vim/vim#14358

0fd560d46a

Co-authored-by: Wu, Zhenyu <wuzhenyu@ustc.edu>

runtime/lua/vim/filetype.lua

@@ -1141,6 +1141,7 @@ local extension = {
   yml = 'yaml',
   yaml = 'yaml',
   eyaml = 'yaml',
+  mplstyle = 'yaml',
   yang = 'yang',
   yuck = 'yuck',
   z8a = 'z8a',