Change submodules path to use HTTPS instead of SSH

.gitmodules

 	url = https://github.com/Unity-Technologies/ShaderGraph
 [submodule "Tests/UTF_Core"]
 	path = Tests/UTF_Core
-	url = git@github.com:Unity-Technologies/UTF_Core.git
+url=https://github.com/Unity-Technologies/UTF_Core.git
-	url = git@github.com:Unity-Technologies/UTF_Tests_HDRP.git
+url=https://github.com/Unity-Technologies/UTF_Tests_HDRP.git