commit-graph: don't consider "replace" objects with "verify"

Extend the code added in d6538246d3 (commit-graph: not compatible
with replace objects, 2018-08-20) which ignored replace objects in the
"write" command to ignore it in the "verify" command too.

We can just move this assignment to the cmd_commit_graph(), it
dispatches to "write" and "verify", and we're unlikely to ever get a
sub-command that would like to consider replace refs.

This will make tests added in eddc1f556c (mktag tests: test
update-ref and reachable fsck, 2021-06-17) pass in combination with
the "GIT_TEST_COMMIT_GRAPH" mode added in 859fdc0c3c (commit-graph:
define GIT_TEST_COMMIT_GRAPH, 2018-08-29), except that mode is
currently broken (but is being fixed concurrently). See the discussion
starting at [1].

1. https://lore.kernel.org/git/87wnmihswp.fsf@evledraar.gmail.com/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit-graph.c

@@ -267,7 +267,6 @@ static int graph_write(int argc, const char **argv)
 	    git_env_bool(GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS, 0))
 		flags |= COMMIT_GRAPH_WRITE_BLOOM_FILTERS;
 
-	read_replace_refs = 0;
 	odb = find_odb(the_repository, opts.obj_dir);
 
 	if (opts.reachable) {
@@ -328,6 +327,7 @@ int cmd_commit_graph(int argc, const char **argv, const char *prefix)
 			     builtin_commit_graph_usage,
 			     PARSE_OPT_STOP_AT_NON_OPTION);
 
+	read_replace_refs = 0;
 	save_commit_buffer = 0;
 
 	if (argc > 0) {

t/t5318-commit-graph.sh

@@ -366,6 +366,7 @@ test_expect_success 'replace-objects invalidates commit-graph' '
 		git commit-graph write --reachable &&
 		test_path_is_file .git/objects/info/commit-graph &&
 		git replace HEAD~1 HEAD~2 &&
+		graph_git_two_modes "commit-graph verify" &&
 		git -c core.commitGraph=false log >expect &&
 		git -c core.commitGraph=true log >actual &&
 		test_cmp expect actual &&