Rollup merge of #143444 - lukas-code:gvn-test, r=RalfJung

clean up GVN TypeId test

addresses https://github.com/rust-lang/rust/pull/142789#discussion_r2184897992

This is an attempt to clarify what this test is actually supposed to test and make it less dependent on `TypeId` internals (it now depends on the output of `type_name` instead).

I verified that this version still miscompiles on `nightly-2025-02-11`.

r? ``@oli-obk`` ``@RalfJung``