Separate arch and ubuntu GH Actions into their own files. Fixes #151

.github/workflows/building.yml → .github/workflows/arch-build.yml

 # This is a basic workflow to help you get started with Actions
 
-name: Building
+name: Check build for Arch.
 
 # Controls when the workflow will run
 on:
@@ -15,15 +15,9 @@ on:
 
 jobs:
   build:
-    strategy:
-      matrix:
-        distro:
-          - archlinux
-          - ubuntu
-
     runs-on: ubuntu-latest
     container:
-      image: erikreider/swaync:${{ matrix.distro }}
+      image: erikreider/swaync:archlinux
     steps:
       - uses: actions/checkout@v2
       - name: Meson configure

.github/workflows/ubuntu-build.yml

+# This is a basic workflow to help you get started with Actions
+
+name: Check build for latest Ubuntu LTS.
+
+# Controls when the workflow will run
+on:
+  # Triggers the workflow on push or pull request events but only for the main branch
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    container:
+      image: erikreider/swaync:ubuntu
+    steps:
+      - uses: actions/checkout@v2
+      - name: Meson configure
+        run: meson build
+      - name: Build
+        run: ninja -C build