t4051: mark supporting files as requiring LF-only line endings

The test t4051-diff-function-context.sh passes on Linux when
core.autocrlf=true even without marking its support files as LF-only,
but they fail when core.autocrlf=true in Git for Windows' SDK.

The reason is that `grep ... >file.c.new` will keep CR/LF line endings
on Linux (obviously treating CRs as if they were regular characters),
but will be converted to LF-only line endings with MSYS2's grep that is
used in Git for Windows.

As we do not want to validate the way the available `grep` works, let's
just mark the input as LF-only and move on.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/.gitattributes

@@ -6,6 +6,7 @@ t[0-9][0-9][0-9][0-9]/* -whitespace
 /t4034/*/* eol=lf
 /t4013/* eol=lf
 /t4018/* eol=lf
+/t4051/* eol=lf
 /t4100/* eol=lf
 /t4101/* eol=lf
 /t4109/* eol=lf