polkadot-primitives: compilation error v8 tests

[jarkkojs]

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Description of bug

I took the compilation error fix away from this PR but it still should be fixed: #6533
(see the reverts in the end).

Steps to reproduce

These errors can been seen in Zed:

[bkchr]

The tests are compiling in CI. So, I don't know what are the compilation errors? Can you replicate these errors with rustc?

IDE's sometimes show "fake" errors, which I think is happening here as well. If you can not reproduce the issue with a cargo build/cargo test command, please close the issue.