gitattributes: Mark *.svg as binary

The goal is to put .svg files under git grep's radar. Otherwise a
pretty innocent 'git grep db::is_local' dumps the contents of the
docs/kb/flamegraph.svg on the screen, because it a) contains the
grep pattern and b) is looooong one-liner

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Message-Id: <20220730090026.8537-1-xemul@scylladb.com>

.gitattributes

@@ -1,2 +1,3 @@
 *.cc diff=cpp
 *.hh diff=cpp
+*.svg binary