ci: update runner to ubuntu-24.04 and refresh test matrix

- ubuntu-20.04 runner image was removed from GitHub Actions in April 2025
- Add Elixir 1.19 (latest stable) and move lint target to 1.19 + OTP 28
- Drop Elixir 1.12, 1.13, 1.14 (no longer in security support upstream)
- Drop OTP < 24.3 since they are not provided on ubuntu-22.04/24.04

Author: k-asm

.github/workflows/ci.yml

@@ -4,17 +4,23 @@ on: [push, pull_request]
 jobs:
   build:
     name: Build and test
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
     env:
       MIX_ENV: test
     # see https://hexdocs.pm/elixir/compatibility-and-deprecations.html#between-elixir-and-erlang-otp
     strategy:
       fail-fast: false
       matrix:
         include:
+          - elixir: 1.19.x
+            otp: 28.x
+            lint: true
+          - elixir: 1.19.x
+            otp: 26.x
           - elixir: 1.18.x
             otp: 27.x
-            lint: true
+          - elixir: 1.18.x
+            otp: 25.x
           - elixir: 1.17.x
             otp: 27.x
           - elixir: 1.17.x
@@ -27,22 +33,6 @@ jobs:
             otp: 26.x
           - elixir: 1.15.x
             otp: 24.x
-          - elixir: 1.14.x
-            otp: 25.x
-          - elixir: 1.14.x
-            otp: 23.x
-          - elixir: 1.13.x
-            otp: 24.x
-          - elixir: 1.13.x
-            otp: 22.x
-          - elixir: 1.12.x
-            otp: 24.x
-          - elixir: 1.12.x
-            otp: 22.x
-          - elixir: 1.11.x
-            otp: 23.x
-          - elixir: 1.11.x
-            otp: 21.x
     steps:
       - uses: actions/checkout@v4
       - uses: erlef/setup-beam@v1