ci: add solc 0.8.x tests

Author: elopez

Diff for: .github/scripts/install-solc.sh

@@ -18,6 +18,7 @@ fetch_all() {
   fetch_solc "0.5.7"
   fetch_solc "0.6.12"
   fetch_solc "0.7.5"
+  fetch_solc "0.8.20"
 }
 
 

Diff for: .github/workflows/ci.yml

@@ -156,7 +156,10 @@ jobs:
           - "0.5.7"
           - "0.6.12"
           - "0.7.5"
+          - "0.8.20"
         include:
+          - solc: "0.8.20"
+            experimental: true
           - os: windows-latest
             experimental: true