fix: regex pattern for file extension detection

[haggishunk]

Fixes error when opening files.

Error detected while processing BufReadPost Autocommands for "*":
Error executing lua callback: ...rew/Cellar/neovim/0.11.5/share/nvim/runtime/filetype.lua:36: BufReadPost Autocommands for "*"..FileType Autocommands
for "*"..Syntax Autocommands for "*"..function <SNR>85_SynSet[26]..script ***/.local/share/nvim/lazy/vim-jinja2-syntax/syntax/jinja.v
im[39]
...
line   39:
E169: Command too recursive
line  112:
E169: Command too recursive
line  139:
E121: Undefined variable: main_syntax
E121: Undefined variable: main_syntax
E121: Undefined variable: main_syntax