vim-patch:9.1.2146: filetype: cel files are not recognized (#37834)

Problem:  filetype: cel files are not recognized
Solution: Detect *.cel files as cel filetype (Stefan VanBuren).

Reference:
https://cel.dev/
e36c49febc/testing/src/test/resources/expressions/coverage_test_case/simple_expression.cel
d0d2dbabae/example.cel

closes: vim/vim#19381

fb5777fa20

Co-authored-by: Stefan VanBuren <svanburen@buf.build>

runtime/lua/vim/filetype.lua

@@ -296,6 +296,7 @@ local extension = {
   cdl = 'cdl',
   toc = detect_line1('\\contentsline', 'tex', 'cdrtoc'),
   cedar = 'cedar',
+  cel = 'cel',
   cfc = 'cf',
   cfm = 'cf',
   cfi = 'cf',