gcore-shaders: fix doctest

Author: Firestar99

Cargo.lock

@@ -25,6 +25,9 @@ serde = { workspace = true, optional = true }
 specta = { workspace = true, optional = true }
 log = { workspace = true, optional = true }
 
+[dev-dependencies]
+graphene-core = { workspace = true }
+
 [lints.rust]
 # the spirv target is not in the list of common cfgs so must be added manually
 unexpected_cfgs = { level = "warn", check-cfg = [