Revert "Update conanfile.py use stable boost"

This reverts commit f2364b57.

conanfile.py

@@ -30,8 +30,8 @@ class ProjectPhoenix(ConanFile):
     settings = "os", "compiler", "build_type", "arch"
 
     requires = (("assimp/4.1.0@RWTH-VR/thirdparty"),
-                ("boost_optional/1.66.0@bincrafters/stable"),
-                ("boost_signals2/1.66.0@bincrafters/stable"), #not yet available in stable, change whenever available (also boost_optional)
+                ("boost_optional/1.66.0@bincrafters/testing"),
+                ("boost_signals2/1.66.0@bincrafters/testing"), #not yet available in stable, change whenever available (also boost_optional)
                 ("catch/1.12.0@RWTH-VR/thirdparty"),
                 ("cppcheck/1.82@RWTH-VR/thirdparty"),
                 ("cpplint/e8ffd7c@RWTH-VR/thirdparty"),