Switch back to ubuntu-20.04 runners, fix AppImage builder exec

.github/workflows/ci.yml

@@ -79,7 +79,7 @@ jobs:
 
   linux-pyinstaller:
     name: Linux (PyInstaller)
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     steps:
       - name: Checkout code
@@ -156,7 +156,7 @@ jobs:
 
   linux-appimage:
     name: Linux (AppImage)
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     steps:
       - name: Checkout code
@@ -191,7 +191,7 @@ jobs:
       - name: Create AppImage
         env:
           APPIMAGE_EXTRACT_AND_RUN: 1
-          APP_VERSION: ${{ steps.vars.outputs.app_version }}.${{ steps.vars.outputs.sha_short }}
+          APP_VERSION: ${{steps.vars.outputs.app_version}}.${{steps.vars.outputs.sha_short}}
         run: |
           ./appimage-builder --recipe appimage/AppImageBuilder.yml