patch 8.2.1432: various inconsistencies in test files

Problem:    Various inconsistencies in test files.
Solution:   Add modelines where they were missing.  Use Check commands instead
            of silently skipping over tests.  Adjust indents and comments.
            (Ken Takata, closes #6695)

src/testdir/test_fileformat.vim

@@ -1,3 +1,4 @@
+" Test for 'fileformat'
 
 " Test behavior of fileformat after bwipeout of last buffer
 func Test_fileformat_after_bw()