[fix][CI] Disable macos-11.0 workflow

Related to actions/runner-images#2381

**Why this change was necessary**
The macOS 11.0 runner is failing to start for an unacceptably long
time. Many other projects are running into the same issue. In the
interim, this build matrix option should be disabled.

**What this change does**
See title.

**Any side-effects?**
None

.github/workflows/poetry-dev.yml

@@ -30,7 +30,7 @@ jobs:
           - 'ubuntu-18.04'
           - 'ubuntu-16.04'
           - 'macos-10.15'
-          - 'macos-11.0'
+          # - 'macos-11.0'
           - 'windows-2019'
           - 'windows-2016'
         python-version: