Switch coverage to ubuntu 18.04

It seems that there is no 16.04 image anymore, since github actions was
not able to find it for 24 hours [1].

  [1]: https://github.com/libevent/libevent/actions/runs/1522612189

diff --git a/.github/workflows/coverage.yml b/.github/workflows/coverage.yml
index 67707bbd578b04b95364f8737ee5d3b77e9971de..f23424dc8e636212558b8083aa6aed85d3b09149 100644 (file)
--- a/.github/workflows/coverage.yml
+++ b/.github/workflows/coverage.yml
@@ -14,7 +14,7 @@ on:
 
 jobs:
   linux:
-    runs-on: ubuntu-16.04
+    runs-on: ubuntu-18.04
     if: "!contains(github.event.head_commit.message, 'ci skip')"
     steps:
       - uses: actions/checkout@v2.0.0