The latest top-of-tree fails to build due to an error in the builder/package_plugins/utils.py code:

```
DEBUG:fromager._main_:245: could not handle install dependency beniget~=0.4.0 (0.4.2.post1) for build-system dependency pythran<0.18.0,>=0.14.0 (0.17.0) for build-system dependency scipy>=1.6.0 (1.15.1) for install dependency scikit-learn>=0.24.1 (1.6.1) for install dependency lm-eval>=0.4.4 (0.4.7) for install dependency instructlab-eval<0.5.0,>=0.4.0 (0.4.2) for toplevel dependency instructlab[rocm]==0.22.1 (0.22.1)
Traceback (most recent call last):
File "/opt/app-root/lib64/python3.11/site-packages/fromager/bootstrapper.py", line 168, in bootstrap
self.bootstrap(dep, RequirementType.INSTALL)
File "/opt/app-root/lib64/python3.11/site-packages/fromager/bootstrapper.py", line 80, in bootstrap
source_url, resolved_version = self._resolve_source_with_history(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/app-root/lib64/python3.11/site-packages/fromager/bootstrapper.py", line 393, in _resolve_source_with_history
source_url, resolved_version = sources.resolve_source(
^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/app-root/lib64/python3.11/site-packages/fromager/metrics.py", line 25, in wrapper_timeit
ret = func(ctx=ctx, req=req, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/app-root/lib64/python3.11/site-packages/fromager/sources.py", line 92, in resolve_source
resolver_results = overrides.find_and_invoke(
^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/app-root/lib64/python3.11/site-packages/fromager/overrides.py", line 52, in find_and_invoke
result = invoke(fn, **kwargs)
^^^^^^^^^^^^^^^^^^^^
File "/opt/app-root/lib64/python3.11/site-packages/fromager/overrides.py", line 71, in invoke
return fn(**kwargs)
^^^^^^^^^^^^
File "/opt/app-root/lib64/python3.11/site-packages/package_plugins/gast.py", line 35, in resolve_source
version = resolve_specifier(ctx, req, version_map)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/app-root/lib64/python3.11/site-packages/package_plugins/utils.py", line 189, in resolve_specifier
raise ValueError(f"Spec must use '==': Operator has {req}")
ValueError: Spec must use '==': Operator has gast>=0.5.0