patch 8.2.3909: Containerfile using prefix name not recognized

Problem:    Containerfile using prefix name not recognized.
Solution:   Recognize Containerfile.*.

runtime/filetype.vim

@@ -2240,7 +2240,7 @@ au BufNewFile,BufRead crontab,crontab.*,*/etc/cron.d/*		call s:StarSetf('crontab
 au BufNewFile,BufRead */etc/dnsmasq.d/*		call s:StarSetf('dnsmasq')
 
 " Dockerfile
-au BufNewFile,BufRead Dockerfile.*		call s:StarSetf('dockerfile')
+au BufNewFile,BufRead Dockerfile.*,Containerfile.*	call s:StarSetf('dockerfile')
 
 " Dracula
 au BufNewFile,BufRead drac.*			call s:StarSetf('dracula')

src/testdir/test_filetype.vim

@@ -146,7 +146,7 @@ let s:filename_checks = {
     \ 'diff': ['file.diff', 'file.rej'],
     \ 'dircolors': ['.dir_colors', '.dircolors', '/etc/DIR_COLORS', 'any/etc/DIR_COLORS'],
     \ 'dnsmasq': ['/etc/dnsmasq.conf', '/etc/dnsmasq.d/file', 'any/etc/dnsmasq.conf', 'any/etc/dnsmasq.d/file'],
-    \ 'dockerfile': ['Containerfile', 'Dockerfile', 'file.Dockerfile', 'Dockerfile.debian'],
+    \ 'dockerfile': ['Containerfile', 'Dockerfile', 'file.Dockerfile', 'Dockerfile.debian', 'Containerfile.something'],
     \ 'dosbatch': ['file.bat', 'file.sys'],
     \ 'dosini': ['.editorconfig', '/etc/pacman.conf', '/etc/yum.conf', 'file.ini', 'npmrc', '.npmrc', 'php.ini', 'php.ini-5', 'php.ini-file', '/etc/yum.repos.d/file', 'any/etc/pacman.conf', 'any/etc/yum.conf', 'any/etc/yum.repos.d/file', 'file.wrap'],
     \ 'dot': ['file.dot', 'file.gv'],

src/version.c

@@ -749,6 +749,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3909,
 /**/
     3908,
 /**/