ci: add Elixir 1.19 support to CI matrix

Add Elixir 1.19 to the test matrix with exclusion for OTP 25
(not compatible per Elixir compatibility table).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: jwaldrip

.github/workflows/ci.yml

@@ -17,13 +17,16 @@ jobs:
           - "1.16"
           - "1.17"
           - "1.18"
+          - "1.19"
         otp:
           - "25"
           - "26"
           - "27"
           - "28"
         # see https://hexdocs.pm/elixir/compatibility-and-deprecations.html#between-elixir-and-erlang-otp
         exclude:
+          - elixir: 1.19
+            otp: 25
           - elixir: 1.17
             otp: 28
           - elixir: 1.16