ci: use jq to construct builds matrix

.github/generate-matrix.py

@@ -1,27 +0,0 @@
-#!/usr/bin/env python3
-import subprocess
-import json
-import sys
-
-
-expr = 'builtins.toJSON (builtins.attrNames (import ./tests {}))'
-
-
-if __name__ == '__main__':
-    attrs = json.loads(json.loads(subprocess.check_output([
-        "nix-instantiate",
-        "--eval",
-        "--expr",
-        expr
-    ])))
-
-    matrix = [
-        {
-            "attr": attr
-        }
-        for attr in attrs
-    ]
-
-    sys.stdout.write("::set-output name=matrix::")
-    json.dump({"include": matrix}, sys.stdout)
-    sys.stdout.flush()

.github/workflows/ci.yml

@@ -26,7 +26,11 @@ jobs:
           nix_path: nixpkgs=channel:nixos-unstable
           extra_nix_config: experimental-features = nix-command
       - id: set-matrix
-        run: ./.github/generate-matrix.py
+        run: |
+          set -euo pipefail
+
+          matrix="$(nix-instantiate --eval --json --expr 'builtins.attrNames (import ./tests {})' | jq '{attr: .}')"
+          echo "::set-output name=matrix::$matrix"
 
   builds:
     needs: matrix_generate