automation: trigger the edera/6.18-lts audit weekly

.github/workflows/lts-audit-trigger.yml

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+name: Trigger edera/6.18-lts audit
+
+# Starts edera/6.18-lts's weekly audit for Edera commits from edera/mainline
+# that it lacks, and does nothing else. The audit runs there, with its own
+# copy of kernel-nightly.yml (audit=true runs lts-audit.yml), and keeps an
+# issue open while anything is missing.
+#
+# GitHub runs scheduled workflows only from the default branch, edera/mainline,
+# so this schedule lives here, like lts-rebase-trigger.yml. It runs after
+# that night's rebases have had time to land.
+
+on:
+  schedule:
+    - cron: '41 9 * * 1' # 09:41 UTC Mondays
+
+permissions: {}
+
+jobs:
+  dispatch:
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    permissions:
+      actions: write
+    steps:
+      - name: Harden runner
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
+        with:
+          egress-policy: audit
+
+      - name: Dispatch
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: gh workflow run kernel-nightly.yml --repo "$GITHUB_REPOSITORY" --ref edera/6.18-lts -f audit=true