test(naga): assert error for ImageStore type mismatch

[mooori]

Connections

#7023

Description

Adds the test to tests/naga/validation.rs, as this seemed to be the simplest way to do it (though I'm new to the codebase). Seems like naga snapshot tests are currently only parsing (not validating) and are not handling (validation) errors (ref).

Testing

cargo nextest run --test naga validation::image_store_type_mismatch

Squash or Rebase?

Squash would be easier if more commits follow, but I'm fine with both.

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy --tests. If applicable, add:
  • --target wasm32-unknown-unknown
• Run cargo xtask test to run tests.
• If this contains user-facing changes, add a CHANGELOG.md entry.

For cargo xtask test, on my machine a few tests fail. I think the failures shouldn't be due to the changes in this PR which only affects items private to tests/naga/validation.rs.