Separate updating webring and building site steps

This enables updating post without interrupting the webring which is
supposed to stay for a week.

.github/workflows/build-webring.yml

@@ -0,0 +1,14 @@
+name: "Update webring"
+on:
+  schedule:
+    # Every Sunday.
+    - cron: '0 0 * * 0'
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: cachix/install-nix-action@v17
+        with:
+          nix_path: nixpkgs=channel:nixpkgs-unstable
+      - run: nix develop -c make build-openring

.github/workflows/build.yml

@@ -3,9 +3,11 @@ on:
   push:
     branches:
       - master
-  schedule:
+  workflow_run:
-    # Every Sunday.
+    workflows:
-    - cron: '0 0 * * 0'
+      - "Update webring"
+    types:
+      - "completed"
 jobs:
   build:
     runs-on: ubuntu-latest

Makefile

@@ -1,5 +1,5 @@
 .PHONY: build
-build: build-openring
+build:
 	hugo --destination public
 
 .PHONY: build-openring