Use getattr for aspect_hints in swift_clang_module_aspect (#1224)

To make supporting Bazel 6 easier use `getattr` to conditionally get the
`aspect_hints` attr. This can be removed when we drop support for Bazel
6 as `aspect_hints` are always available as an attr in Bazel 7+

swift/internal/swift_clang_module_aspect.bzl

@@ -764,7 +764,8 @@ def _find_swift_interop_info(target, aspect_ctx):
     # We don't break this loop early when we find a matching hint, because we
     # want to give an error message if there are two aspect hints that provide
     # `_SwiftInteropInfo` (or if both the rule and an aspect hint do).
-    for hint in aspect_ctx.rule.attr.aspect_hints:
+    # TODO: remove usage of `getattr` and use `aspect_ctx.rule.attr.aspect_hints` directly when we drop Bazel 6.
+    for hint in getattr(aspect_ctx.rule.attr, "aspect_hints", []):
         if _SwiftInteropInfo in hint:
             if interop_target:
                 if interop_from_rule: