patch 9.0.1422: Sage files are not recognized

Problem:    Sage files are not recognized.
Solution:   Add a pattern for Sage files. (Amaan Qureshi, closes #12176)

Author: amaanq

runtime/filetype.vim

@@ -1811,6 +1811,9 @@ au BufNewFile,BufRead Cargo.lock,*/.cargo/config,*/.cargo/credentials	setf toml
 " S-lang (or shader language, or SmallLisp)
 au BufNewFile,BufRead *.sl			setf slang
 
+" Sage
+au BufNewFile,BufRead *.sage			setf sage
+
 " Samba config
 au BufNewFile,BufRead smb.conf			setf samba
 

src/testdir/test_filetype.vim

@@ -540,6 +540,7 @@ let s:filename_checks = {
     \ 'skill': ['file.il', 'file.ils', 'file.cdf'],
     \ 'cdc': ['file.cdc'],
     \ 'slang': ['file.sl'],
+    \ 'sage': ['file.sage'],
     \ 'slice': ['file.ice'],
     \ 'slpconf': ['/etc/slp.conf', 'any/etc/slp.conf'],
     \ 'slpreg': ['/etc/slp.reg', 'any/etc/slp.reg'],

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1422,
 /**/
     1421,
 /**/