vim-patch:9.0.1668: PEM files are not recognized (#24169)

Problem:    PEM files are not recognized.
Solution:   Add patterns to match PEM files. (closes vim/vim#12582)

0256d76a33

runtime/lua/vim/filetype.lua

@@ -783,6 +783,10 @@ local extension = {
   g = 'pccts',
   pcmk = 'pcmk',
   pdf = 'pdf',
+  pem = 'pem',
+  cer = 'pem',
+  crt = 'pem',
+  csr = 'pem',
   plx = 'perl',
   prisma = 'prisma',
   psgi = 'perl',

test/old/testdir/test_filetype.vim

@@ -466,6 +466,7 @@ func s:GetFilenameChecks() abort
     \ 'pccts': ['file.g'],
     \ 'pcmk': ['file.pcmk'],
     \ 'pdf': ['file.pdf'],
+    \ 'pem': ['file.pem', 'file.cer', 'file.crt', 'file.csr'],
     \ 'perl': ['file.plx', 'file.al', 'file.psgi', 'gitolite.rc', '.gitolite.rc', 'example.gitolite.rc', '.latexmkrc', 'latexmkrc'],
     \ 'pf': ['pf.conf'],
     \ 'pfmain': ['main.cf', 'main.cf.proto'],