build(#2772): declare enumflags2 at the workspace level

`cargo add -p hive-jobq` wrote the version into the crate's own manifest
instead of `[workspace.dependencies]`, which is how every other shared
dep here is declared and the thing that stops two members drifting onto
different versions of the same crate.

hive-jobq/Cargo.toml

@@ -9,7 +9,7 @@ workspace = true
 
 [dependencies]
 chrono = { workspace = true }
-enumflags2 = { version = "0.7.12", features = ["serde"] }
+enumflags2.workspace = true
 serde = { workspace = true }
 thiserror = { workspace = true }