target Ubuntu Bionic in PPA release (#1909)

.github/workflows/release.yml

@@ -207,7 +207,7 @@ jobs:
   ppa:
     name: Upload source package to PPA
     needs: [buildkit, metadata]
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
     steps:
       - uses: actions/checkout@v2
       - name: install build tools

dist/linux/debian/changelog

@@ -1,4 +1,4 @@
-cryptomator (${PPA_VERSION}) focal; urgency=low
+cryptomator (${PPA_VERSION}) bionic; urgency=low
 
   * Full changelog can be found on https://github.com/cryptomator/cryptomator/releases