ci: fix wrong parameter enumeration in matrix configuration

Signed-off-by: oleg.hoefling <[email protected]>

Author: hoefling

.github/workflows/tests.yml

@@ -10,7 +10,7 @@ jobs:
   build:
     strategy:
       matrix:
-        os: ubuntu-latest
+        os: [ubuntu-latest]
         python-version: [3.7, 3.8, 3.9, '3.10', '3.11']
         include:
           - os: ubuntu-20.04