ci: cargo-outdated (dtolnay style)

This checks if there are outdated dependencies every day at 04:45, an
arbitrarily chosen time that has nothing to do with my problematic sleep
schedule.

In an ideal world, everyone that needs to know this would then be
watching this repository, and be notified if this workflow fails (since
it doesn't open a PR, which is our current method of notification), but
hey, if not I'll just fix it, it's not horrible to do anyway /shrug

Signed-off-by: Christina Sørensen <christina@cafkafk.com>

.github/workflows/cargo-outdated.yml

@@ -0,0 +1,18 @@
+# SPDX-FileCopyrightText: 2024 Christina Sørensen
+#
+# SPDX-License-Identifier: EUPL-1.2
+
+name: outdated
+on:
+  schedule: [{cron: "45 4 * * *"}]
+jobs:
+  outdated:
+    name: Outdated
+    runs-on: ubuntu-latest
+    if: github.event_name != 'pull_request'
+    timeout-minutes: 45
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/install@cargo-outdated
+      - run: cargo outdated --workspace --exit-code 1
+      - run: cargo outdated --manifest-path fuzz/Cargo.toml --exit-code 1