core: force version 18.04 of Ubuntu in CI

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a65ebada59a712464ad328b1dff0d929f69831ff..448ee651749a2f865864e4c7c02b47b89d401627 100644 (file)
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -7,7 +7,7 @@ jobs:
   build:
 
     name: ${{ matrix.config.name }}
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
     strategy:
       fail-fast: false
       matrix: