Waf build system: fix typo in legacy_attributes (#33958)

Fix erroneous duplication of `build_time_test_callbacks` in
`legacy_attributes`: one of the duplicates should be
`install_time_test_callbacks`

lib/spack/spack/build_systems/waf.py

@@ -72,9 +72,9 @@ class WafBuilder(BaseBuilder):
 
     #: Names associated with package attributes in the old build-system format
     legacy_attributes = (
-        "build_time_test_callbacks",
         "build_time_test_callbacks",
         "build_directory",
+        "install_time_test_callbacks",
     )
 
     # Callback names for build-time test