Use proper encoding for email fixtures.

.gitattributes

@@ -1,6 +1,9 @@
 # Set default behaviour, in case users don't have core.autocrlf set.
 * text=auto
 
+# Treat email fixtures as binary files so CRLF are not converted to LF.
+*.eml binary
+
 # Explicitly declare text files we want to always be normalized and converted
 # to native line endings on checkout.
 *.yml text