Fix auto cargo updates

I was messing around with `cargo audit` and `cargo outdated` and realized I
broke the auto-update of cargo.

When I switched from using `cargo update` to `cargo upgrade`, I didn't realize
that `cargo upgrade` doesn't update the `Cargo.lock` file.

I only noticed because `cargo audit` was reporting a yanked version of libc and
running `cargo update` fixed it.

I added running `cargo outdated` as a sanity check that things are updating
correcty.

default.nix

@@ -109,6 +109,8 @@ let
             ];
             text = ''
               echo "<details><summary>cargo changes</summary>"
+              echo ""
+              echo "### cargo upgrade"
               printf "\n\`\`\`\n"
               # --incompatible allows jumping to the next major version.
               cargo upgrade --incompatible --manifest-path "$1/Cargo.toml" 2>&1