diffguard-testkit/fixtures.rs:17,784: 2 more wildcard use super::* in test modules

[EffortlessSteven]

Continuing the cleanup from #589, there are two more use super::* wildcard imports in test modules in fixtures.rs:

Line 17 — in pub mod sample_configs:

pub mod sample_configs {
    use super::*;  // wildcard import from parent

Line 784 — in #[cfg(test)] mod tests:

#[cfg(test)]
mod tests {
    use super::*;  // wildcard import from parent

Both are test modules where clippy's wildcard_imports lint fires at pedantic level. While #[allow] is defensible here, explicit imports (as suggested in the clippy fix) improve readability and make it obvious what traits/types are actually used.

Compare with the existing fix in #589 which addressed fixtures.rs:608 and xtask/conform_real.rs:1437.

Fix: Replace use super::*; with explicit use super::{CheckReceipt, ConfigFile, ...}; etc., using the clippy suggestion.