exclude all macosx job but one

Author: RCasatta

.github/workflows/test.yml

@@ -12,8 +12,11 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-20.04, macos-10.15 ]
+        os: [ ubuntu-20.04 ]
         feature: [ "0_21_1", "0_21_0", "0_20_1", "0_20_0", "0_19_1", "0_19_0_1", "0_18_1", "0_18_0", "0_17_1"]
+        include:
+          - os: "macos-10.15"
+            feature: "0_21_1"
 
     steps:
       - uses: actions/checkout@v2