clone: don't rely on auto-saving for single-branch

The code used to rely on the clone code calling the remote's save, which
does not happen anymore, meaning that the configuration settings the
remote expected were not being written to disk.

The run-time configuration was still being affected, so the right branch
was being cloned. The tests continued to pass as we did not check for
the configuration entires. Fix this by creating the remote with the
single-branch refspec we want and checking for its existence in the
configuration.

tests/online/remotes.c

 #include "clar_libgit2.h"
 
+static const char *refspec = "refs/heads/first-merge:refs/remotes/origin/first-merge";
+
 static int remote_single_branch(git_remote **out, git_repository *repo, const char *name, const char *url, void *payload)
 {
-	char *fetch_refspecs[] = {
-		"refs/heads/first-merge:refs/remotes/origin/first-merge",
-	};
-	git_strarray fetch_refspecs_strarray = {
-		fetch_refspecs,
-		1,
-	};
-
 	GIT_UNUSED(payload);
 
-	cl_git_pass(git_remote_create(out, repo, name, url));
-	cl_git_pass(git_remote_set_fetch_refspecs(*out, &fetch_refspecs_strarray));
+	cl_git_pass(git_remote_create_with_fetchspec(out, repo, name, url, refspec));
 
 	return 0;
 }
@@ -22,6 +15,7 @@ void test_online_remotes__single_branch(void)
 {
 	git_clone_options opts = GIT_CLONE_OPTIONS_INIT;
 	git_repository *repo;
+	git_remote *remote;
 	git_strarray refs;
 	size_t i, count = 0;
 
@@ -38,6 +32,15 @@ void test_online_remotes__single_branch(void)
 	cl_assert_equal_i(1, count);
 
 	git_strarray_free(&refs);
+
+	cl_git_pass(git_remote_lookup(&remote, repo, "origin"));
+	cl_git_pass(git_remote_get_fetch_refspecs(&refs, remote));
+
+	cl_assert_equal_i(1, refs.count);
+	cl_assert_equal_s(refspec, refs.strings[0]);
+
+	git_strarray_free(&refs);
+	git_remote_free(remote);
 	git_repository_free(repo);
 }