PR checks: stop running unset-env on two old CLI versions

Looks like there was a bug in the oldest two CLI versions, on `macos-12` here.

.github/workflows/__unset-environment.yml

@@ -28,20 +28,16 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: macos-12
-            version: stable-20230403
-          - os: macos-12
-            version: stable-v2.13.5
           - os: macos-12
             version: stable-v2.14.6
           - os: macos-latest
             version: stable-v2.15.5
           - os: macos-latest
             version: stable-v2.16.6
-          - os: macos-latest
-            version: default
           - os: macos-latest
             version: latest
+          - os: macos-latest
+            version: default
           - os: macos-latest
             version: nightly-latest
     name: Test unsetting environment variables