wip as string.

.github/workflows/build-ci.yml

@@ -11,9 +11,9 @@ jobs:
     runs-on: ${{matrix.os}}
     strategy:
       matrix:
-        php: [7.1, 7.2, 7.3, 7.4]
+        php: ['7.1', '7.2', '7.3', '7.4']
         os: ['ubuntu-latest']
-        mongodb: [3.6, 4.0, 4.2]
+        mongodb: ['3.6', '4.0', '4.2']
     services:
       mongo:
         image: mongo:${{ matrix.mongodb }}