builtin/annotate: fix leaking args vector

We're leaking the args vector in git-annotate(1) because we never clear
it. Fixing it isn't as easy as calling `strvec_clear()` though because
calling `cmd_blame()` will cause the underlying array to be modified.
Instead, we also need to pass a shallow copy of the argv array to the
function.

Do so to plug the memory leaks.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t8001-annotate.sh

@@ -5,6 +5,7 @@ GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
 TEST_CREATE_REPO_NO_TEMPLATE=1
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 PROG='git annotate'