[adopted] .gitmodules: Change pybind11 URL from relative to absolute (#1101)

All the other URLs are absolute, so logically this one should match.
Additionally, the relative URL will break if someone's main remote is
not on GitHub.

Adopted PR from #1100 - thanks @0cjs!

Co-authored-by: Curt J. Sampson <[email protected]>
Co-authored-by: Roberto Rosmaninho <[email protected]>
Co-authored-by: rv-jenkins <[email protected]>

Author: 4 people

.gitmodules

@@ -6,7 +6,7 @@
 	url = https://github.com/Tencent/rapidjson
 [submodule "deps/pybind11"]
 	path = deps/pybind11
-	url = ../../pybind/pybind11
+	url = https://github.com/pybind/pybind11
 	branch = stable
 [submodule "deps/fmt"]
 	path = deps/fmt