Discard insufficient fork markers (#10682)
In #10669, a pyproject.toml with requires-python but no environment had
a lockfile covering only a subset of the requires-python space:
```toml
resolution-markers = [
"python_full_version >= '3.10' and platform_python_implementation == 'CPython'",
"python_full_version == '3.9.*'",
"python_full_version < '3.9'",
]
```
This marker set is invalid, we have to reject the lockfile. (We can
still use the versions though, to avoid churn).
Part 1/2 of #10669
