[Bugfix] Fix issue with apple framewords and CMake cached variables

[jgsogo]

Changelog: Bugfix: Each Apple framework found using CMake find_library is stored in a different CONAN_FRAMEWORK_<name>_FOUND variable
Docs: omit

Fixes #6035

find_library is not executed if the returning variable to assign already has a value. This PR gives a new name for each variable in the for-loop so the find_library is actually executed for each framework name.

This PR complements #6003

[lasote]

Try to add a test with 2 frameworks and see works ok