Build on Ubuntu 20.04, to match core20.

Author: yossigo

.github/workflows/tags.yml

@@ -7,7 +7,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     if: github.repository == 'redis/redis-snap'
     steps:
     - uses: actions/checkout@v2

.github/workflows/unstable.yml

@@ -7,7 +7,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     if: github.repository == 'redis/redis-snap'
     steps:
     - uses: actions/checkout@v2