add lychee link checker

.gitea/workflows/checks-impure.yaml

@@ -1,12 +0,0 @@
-name: checks-impure
-on:
-  pull_request:
-  push:
-    branches: main
-jobs:
-  test:
-    if: ${{ github.actor != 'ui-asset-bot' }}
-    runs-on: nix
-    steps:
-      - uses: actions/checkout@v3
-      - run: nix run .#impure-checks

.gitea/workflows/checks.yaml

@@ -2,11 +2,21 @@ name: checks
 on:
   pull_request:
   push:
-    branches: main
+    branches:
+      - main
 jobs:
-  test:
+  checks:
-    if: ${{ github.actor != 'ui-asset-bot' }}
     runs-on: nix
     steps:
       - uses: actions/checkout@v3
       - run: nix run --refresh github:Mic92/nix-fast-build -- --no-nom --eval-workers 20
+  check-links:
+    runs-on: nix
+    steps:
+      - uses: actions/checkout@v3
+      - run: nix run --refresh --inputs-from .# nixpkgs#lychee .
+  checks-impure:
+    runs-on: nix
+    steps:
+      - uses: actions/checkout@v3
+      - run: nix run .#impure-checks