patch 9.0.1419: Lean files are not recognized

Problem:    Lean files are not recognized.
Solution:   Add a pattern for Lean files. (Amaan Qureshi, closes #12177)

runtime/filetype.vim

@@ -1112,6 +1112,9 @@ au BufNewFile,BufRead *.ldif			setf ldif
 " Ld loader
 au BufNewFile,BufRead *.ld			setf ld
 
+" Lean
+au BufNewFile,BufRead *.lean			setf lean
+
 " Ledger
 au BufRead,BufNewFile *.ldg,*.ledger,*.journal			setf ledger
 

src/testdir/test_filetype.vim

@@ -320,6 +320,7 @@ let s:filename_checks = {
     \ 'latte': ['file.latte', 'file.lte'],
     \ 'ld': ['file.ld'],
     \ 'ldif': ['file.ldif'],
+    \ 'lean': ['file.lean'],
     \ 'ledger': ['file.ldg', 'file.ledger', 'file.journal'],
     \ 'less': ['file.less'],
     \ 'lex': ['file.lex', 'file.l', 'file.lxx', 'file.l++'],

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1419,
 /**/
     1418,
 /**/