Don't run cov on osx + windows

Author: JacksonMaxfield

.github/workflows/ci-osx.yaml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.6.1", "3.7", "3.8", "3.9"]
+        python-version: ["3.6", "3.7", "3.8", "3.9"]
 
     steps:
       - name: Checkout source
@@ -45,4 +45,4 @@ jobs:
         shell: "bash -l {0}"
         run: |
           conda activate env
-          pytest -v --cov=numcodecs numcodecs
+          pytest -v --pyargs numcodecs

.github/workflows/ci-windows.yaml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.6.1", "3.7", "3.8", "3.9"]
+        python-version: ["3.6", "3.7", "3.8", "3.9"]
 
     steps:
       - name: Checkout source
@@ -45,4 +45,4 @@ jobs:
         shell: "bash -l {0}"
         run: |
           conda activate env
-          pytest -v --cov=numcodecs numcodecs
+          pytest -v --pyargs numcodecs