Move actions to their own file.

.github/workflows/Makefile

@@ -1,3 +1,3 @@
 all:
-	cue export --out yaml ci.cue > ci.yaml
+	cue export --out yaml > ci.yaml
 

.github/workflows/actions.cue

@@ -0,0 +1,37 @@
+package actions
+
+#Name: string
+#Branches: branches: [...string]
+#Tags: tags: [...string]
+
+#On: {
+	push?:         #Branches
+	pull_request?: #Branches
+	page_build?:   #Branches
+}
+
+#Action: "actions/checkout@v2" | "erlef/setup-beam@v1"
+#Uses: {
+	uses: #Action
+	with?: {
+		...
+	}
+}
+#Run: {
+	name: string
+	run:  string
+}
+#Steps: #Uses | #Run
+
+#OS_Version: *"ubuntu-latest" | "macos-latest" | "windows_latest"
+
+#Jobs: ci: {
+	name:      string
+	"runs-on": string
+	strategy:
+		matrix: {
+			otp_vsn: [...string]
+			os: [...#OS_Version]
+		}
+	steps: [...#Steps]
+}

.github/workflows/ci.cue

@@ -1,3 +1,5 @@
+package actions
+
 // Versions for simplicity
 _versions: {
 	latest: ["24.0"]