Use Gleam v0.8.0-rc1 on CI

Author: lpil

.github/workflows/ci.yml

@@ -17,6 +17,6 @@ jobs:
           otp-version: 22.2
       - uses: gleam-lang/[email protected]
         with:
-          gleam-version: 0.7.0
+          gleam-version: 0.8.0-rc1
       - run: rebar3 install_deps
       - run: rebar3 eunit