Fix: more versioning around nightly and maint/main (#359)

* Test Elixir main-otp-28 / Erlang maint-28

* Test Gleam nightly / OTP 28

* Tweak versioning

1. stop trying to "coerce" versions on input
2. handle `OTP-` in one more place
3. handle `nightly`

* Remove tests that should be failing previously

There is no strict 27 for macos-15, for example

* Remove similar tests

We'll test once per platform in similar conditions

* `await` for `assert.rejects` (not noticeable if alone inside `it`)

* Test maint- for strict and loose

.github/workflows/macos.yml

@@ -43,12 +43,6 @@ jobs:
             elixir-version: '1.14.3'
             os: 'macos-latest'
             version-type: 'strict'
-          - otp-version: '27'
-            os: 'macos-15'
-            version-type: 'strict'
-          - otp-version: '26'
-            os: 'macos-15'
-            version-type: 'strict'
           - otp-version: '25'
             os: 'macos-15'
           - otp-version: '26'

.github/workflows/ubuntu.yml

@@ -53,12 +53,6 @@ jobs:
             elixir-version: '1.14.3'
             os: 'ubuntu-latest'
             version-type: 'strict'
-          - otp-version: '27'
-            os: 'ubuntu-24.04'
-            version-type: 'strict'
-          - otp-version: '26'
-            os: 'ubuntu-24.04'
-            version-type: 'strict'
           - otp-version: '25'
             os: 'ubuntu-24.04'
           - otp-version: '26'