Test on OTP-26, drop pre-OTP-23; OTP-27 not compatible yet

Author: seriyps

.github/workflows/ci.yml

@@ -19,15 +19,14 @@ jobs:
       matrix:
         os:
           - "ubuntu-20.04"
-        rebar3: ["3.18.0"]
+        rebar3: ["3.20.0"]
         otp:
-          - "25.1"
+          - "26.2"
+          - "25.3"
           - "24.3"
-          - "23.3"
-          - "22.3"
         include:
-          - otp: "21.3"
-            rebar3: "3.15.2"
+          - otp: "23.3"
+            rebar3: "3.18.0"
             os: "ubuntu-20.04"
     env:
       SHELL: /bin/sh            # needed for erlexec