Try adding empty string variables to the matrix

Author: notroj

.github/workflows/linux.yml

@@ -30,11 +30,11 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest]
-        config: []
+        config: [""]
         name: [Default]
-        pkgs: []
-        env: []
-        notest-cflags: []
+        pkgs: [""]
+        env: [""]
+        notest-cflags: [""]
         include:
           # -------------------------------------------------------------------------
           - name: Empty APLOGNO() test