Update Gleam version on CI

Author: lpil

.github/workflows/test.yml

@@ -16,7 +16,7 @@ jobs:
           otp-version: 22.2
       - uses: gleam-lang/[email protected]
         with:
-          gleam-version: 0.11.2
+          gleam-version: 0.12.1
       - run: rebar3 install_deps
       - run: rebar3 eunit
       - run: gleam format --check src test