Append to the file associations configuration file, instead of replacing it.

Will-fix: #10798

config/chroot_local-hooks/59-file_associations

@@ -12,5 +12,5 @@ if grep -E '^application/pgp-keys=' "$defaults_file"; then
 else
    # XXX: Stretch -- this fixes Tails#10571, unreproducible on non-Tails sid
    echo 'application/pgp-keys=seahorse-pgp-keys.desktop' \
-	> "$defaults_file"
+	>> "$defaults_file"
 fi