ci: update PA version test set

forgot this upon bumping OS.

Author: jnqnfe

.github/workflows/test.yml

@@ -49,10 +49,9 @@ jobs:
     env:
       # Version feature flags to test with `cargo check`
       #
-      # TODO: add pa_v14 and pa_v15 once environment supports it
-      PA_BUILD_VERSIONS: "pa_v13 pa_v12 pa_v8 pa_v6 pa_v5"
+      PA_BUILD_VERSIONS: "pa_v15 pa_v14 pa_v13 pa_v12 pa_v8 pa_v6 pa_v5"
       # Single feature flag to use for `cargo test` steps
-      PA_TEST_VERSION: pa_v13
+      PA_TEST_VERSION: pa_v15
 
     steps:
       - name: Checkout code