ci: add fleet-lint and fix its zizmor finding

.github/workflows/fleet-lint.yaml

@@ -0,0 +1,21 @@
+name: fleet-lint
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+permissions: {}
+
+jobs:
+  fleet-lint:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          fetch-depth: 0 # gitleaks scans every commit of the PR
+          persist-credentials: false
+      - uses: kleinbem/actions/nix-setup@fac6dda312df4b995db2fff7e8552945104b050c # v1.3.0
+      - uses: kleinbem/actions/lint@fac6dda312df4b995db2fff7e8552945104b050c # v1.3.0

.github/workflows/validate.yaml

@@ -13,6 +13,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
       - name: Check .coderabbit.yaml against CodeRabbit's schema
         run: |
           curl -fsSL https://coderabbit.ai/integrations/schema.v2.json -o /tmp/schema.json