CI: Update GitHub actions environments and used actions

Updates the used actions to their latest versions, and update the images to the -latest tags.

This currently means Ubuntu will use 20.04 LTS (and soon 22.04 LTS) and macOS will use macOS 12.

Also adds a workflow_dispatch trigger to the main workflow (the others already have it).

.github/workflows/appimage.yml

@@ -10,16 +10,17 @@ on:
     branches:
       - dev
   workflow_dispatch:
+
 jobs:
   build:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
         build_type: [release]
     steps:
       - name: Checkout source
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           fetch-depth: 0
 
@@ -88,7 +89,7 @@ jobs:
 
       - name: Restore AppImage tools from cache
         id: appimage-tools-cache
-        uses: actions/cache@v2
+        uses: actions/cache@v3
         with:
           key: appimage-tools-1
           path: |
@@ -138,7 +139,7 @@ jobs:
           echo "ARTIFACT_NAME=$ARTIFACT_NAME" >> $GITHUB_ENV
 
       - name: Upload artifacts
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v3
         with:
           name: ${{env.ARTIFACT_NAME}}.AppImage
           path: ${{github.workspace}}/build/${{env.ARTIFACT_NAME}}.AppImage