test matrix syntax

.github/workflows/test_matrix.yml

@@ -0,0 +1,15 @@
+name: test matrix
+
+on:
+  workflow_dispatch:
+
+jobs:
+  test-single:
+    runs-on: linux
+    steps:
+      - run: echo "Single label works"
+  
+  test-array:
+    runs-on: [self-hosted, linux]
+    steps:
+      - run: echo "Array label works"