chore(test): pin loom to a SHA

This pins loom to tokio-rs/loom@555b52fdb267964f0950a52be87b0f28c40b054c
which should fix the CI build (we were previously pointed at a branch
that's deleted since it merged)

Signed-off-by: Eliza Weisman <[email protected]>

Cargo.toml

@@ -37,7 +37,7 @@ lto = true
 opt-level = 3
 
 [patch.crates-io]
-loom = { git = "https://github.com/tokio-rs/loom", branch = "eliza/fix-double-panic-in-drop" }
+loom = { git = "https://github.com/tokio-rs/loom", rev = "555b52fdb267964f0950a52be87b0f28c40b054c" }
 
 [package.metadata.docs.rs]
 all-features = true