tests: network: add missing include for git_repository_new

A newly added test uses the `git_repository_new` function without the
corresponding header file being included. While this works due to the
compiler deducing the correct function signature, we should obviously
just include the function's declaration file.

tests/network/remote/local.c

@@ -2,6 +2,7 @@
 #include "buffer.h"
 #include "path.h"
 #include "posix.h"
+#include "git2/sys/repository.h"
 
 static git_repository *repo;
 static git_buf file_path_buf = GIT_BUF_INIT;