Fix trybuild not having terminal color

.github/workflows/nix.yml

@@ -28,6 +28,6 @@ jobs:
           cmd-format: nix develop ./tests -c {0}
 
       - run: |
-          nix develop -c cargo check --color always
-          nix develop -c cargo test --color always
+          nix develop -c cargo check
+          nix develop -c cargo test
         working-directory: tests

tests/flake.nix

@@ -23,6 +23,7 @@
             pkg-config
             rust-bin.stable.latest.minimal
           ];
+          CARGO_TERM_COLOR = "always";
         };
       }
     );