Get rid of context for exceptions outside PackageBase (#33887)

lib/spack/spack/build_environment.py

@@ -1269,6 +1269,8 @@ def make_stack(tb, stack=None):
             obj = frame.f_locals["self"]
             if isinstance(obj, spack.package_base.PackageBase):
                 break
+    else:
+        return None
 
     # We found obj, the Package implementation we care about.
     # Point out the location in the install method where we failed.