[BUG]: Distinct classes with the same name but in separate anonymous namespaces considered duplicates

[dyollb]

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What version (or hash if on master) of pybind11 are you using?

master

Problem description

Distinct classes with the same name but in separate anonymous namespaces trigger

ImportError: generic_type: type "Foo" is already registered!

This seems to be a new behavior in the current master branch and did not happen in 2.13.6.

I came across this issue when I was preparing a PR for pybind11-stubgen to update to v3.

Reproducible example code

Register a class in two different compilation units:

namespace {
class Foo {};
}

TEST_SUBMODULE(class, m) {
    py::class_<Foo>(m, "Foo");
}

Is this a regression? Put the last known working version here if it is.

This worked in v2.13.6