use strbuf_addstr() instead of strbuf_addf() with "%s", part 2

use strbuf_addstr() instead of strbuf_addf() with "%s", part 2

Replace uses of strbuf_addf() for adding strings with more lightweight
strbuf_addstr() calls.  This is shorter and makes the intent clearer.

bc57b9c0cc5a123365a922fa1831177e3fd607ed already converted three cases,
this patch covers two more.

A semantic patch for Coccinelle is included for easier checking for
new cases that might be introduced in the future.

Signed-off-by: Rene Scharfe <redacted>
Signed-off-by: Junio C Hamano <redacted>