Add build and test for openssl-3.0 (#961)

Add GitHub action that builds and runs tests using openssl-3.0 (default
version in ubuntu 22.04)

It is expected to fail until openssl-3.0 compatibility is introduced
(#955)

A change in cmake action is to make sure we actually run ubuntu:20.04
(which uses openssl-1.1.1). Otherwise, GH will change the version of
ubuntu-latest at some point and it might not be very visible

.github/workflows/cmake.yaml

@@ -12,7 +12,7 @@ env:
 jobs:
   build:
 
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     steps:
     - name: Install dependencies

.github/workflows/tests.yml

@@ -7,10 +7,12 @@ on:
     types: [ opened, reopened, synchronize ]
 
 jobs:
-  build:
-
-    runs-on: ubuntu-latest
-
+  builds:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-20.04, ubuntu-22.04]
+    runs-on: ${{ matrix.os }}
     steps:
     - name: Install dependencies
       run: |