fix: reduce target collision in add_submodule mode (#2423)

* fix: reduce target collision in add_submodule mode

Closes #2420

* fix: update CMakeLists.txt
diff --git a/tools/pybind11Config.cmake.in b/tools/pybind11Config.cmake.in
index 4f0500a..3f11172 100644
--- a/tools/pybind11Config.cmake.in
+++ b/tools/pybind11Config.cmake.in
@@ -130,6 +130,11 @@
 
 include("${CMAKE_CURRENT_LIST_DIR}/pybind11Targets.cmake")
 
+# Easier to use / remember
+add_library(pybind11::headers IMPORTED INTERFACE)
+set_target_properties(pybind11::headers PROPERTIES INTERFACE_LINK_LIBRARIES
+                                                   pybind11::pybind11_headers)
+
 include("${CMAKE_CURRENT_LIST_DIR}/pybind11Common.cmake")
 
 if(NOT pybind11_FIND_QUIETLY)