Make the check for set_cfg_modifiers more repo friendly

Summary:
In other repos, this file is not guaranteed to be at `fbcode/buck2/cfg/experimental/set_cfg_modifiers.bzl`.

For example, in WAIPhone, it is at `tools/buck2/fbcode/buck2/cfg/experimental/set_cfg_modifiers.bzl` and this fails the check.

```
    5: Traceback (most recent call last):
         * tools/buck2/prelude/PACKAGE:15, in <module>
             set_cfg_modifiers(cfg_modifiers = [
         * tools/buck2/fbcode/buck2/cfg/experimental/set_cfg_modifiers.bzl:34, in set_cfg_modifiers
             _set_cfg_modifiers(cfg_modifiers, extra_cfg_modifiers_per_rule)
         * tools/buck2/prelude/cfg/modifier/set_cfg_modifiers.bzl:42, in set_cfg_modifiers
             fail("set_cfg_modifiers is only allowed to be used from a PACKAGE or BUCK_TRE...
       error: fail: set_cfg_modifiers is only allowed to be used from a PACKAGE or BUCK_TREE file, not a bzl file.
         --> tools/buck2/prelude/cfg/modifier/set_cfg_modifiers.bzl:42:13
          |
       42 |             fail("set_cfg_modifiers is only allowed to be used from a PACKAGE or BUCK_TREE file, not a bzl file.")
          |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
          |
```

Since this file must be in the `fbcode` cell (due to loads elsewhere), assume that the file path ends with the path.

Reviewed By: JakobDegen

Differential Revision: D65290874

fbshipit-source-id: 3dd64f27989a9789b30ae56a6492d1571c4ce9c0

prelude/cfg/modifier/set_cfg_modifiers.bzl

@@ -36,7 +36,7 @@ def set_cfg_modifiers(
     if not _is_buck_tree_file(frame1.module_path):
         # Now check the old bzl file for `set_cfg_modifiers` in case it is invoked through that one.
         frame2 = call_stack_frame(2)
-        if not (frame2 and frame1.module_path == "fbcode/buck2/cfg/experimental/set_cfg_modifiers.bzl" and _is_buck_tree_file(frame2.module_path)):
+        if not (frame2 and frame1.module_path.endswith("fbcode/buck2/cfg/experimental/set_cfg_modifiers.bzl") and _is_buck_tree_file(frame2.module_path)):
             fail("set_cfg_modifiers is only allowed to be used from a PACKAGE or BUCK_TREE file, not a bzl file.")
 
     cfg_modifiers = cfg_modifiers or []