Add a mention of git_required label to skil tests also in case of network issues (#4851)

Author: LocutusOfBorg

README.md

@@ -1883,6 +1883,8 @@ json/tests/src/make_test_data_available.hpp:23: FATAL ERROR: REQUIRE( utils::che
 
 In case you have downloaded the library rather than checked out the code via Git, test `cmake_fetch_content_configure` will fail. Please execute `ctest -LE git_required` to skip these tests. See [issue #2189](https://github.com/nlohmann/json/issues/2189) for more information.
 
+Some tests are requiring network to be properly execute. They are labeled as `git_required`. Please execute `ctest -LE git_required` to skip these tests. See [issue #4851](https://github.com/nlohmann/json/issues/4851) for more information.
+
 Some tests change the installed files and hence make the whole process not reproducible. Please execute `ctest -LE not_reproducible` to skip these tests. See [issue #2324](https://github.com/nlohmann/json/issues/2324) for more information. Furthermore, assertions must be switched off to ensure reproducible builds (see [discussion 4494](https://github.com/nlohmann/json/discussions/4494)).
 
 Note you need to call `cmake -LE "not_reproducible|git_required"` to exclude both labels. See [issue #2596](https://github.com/nlohmann/json/issues/2596) for more information.