test_runner: don't create artifacts if Allure is not enabled (#8580)

## Problem

`allure_attach_from_dir` method might create `tar.zst` archives even
if `--alluredir` is not set (i.e. Allure results collection is disabled)

## Summary of changes
- Don't run `allure_attach_from_dir` if `--alluredir`  is not set

test_runner/fixtures/neon_fixtures.py

@@ -4529,6 +4529,13 @@ def test_output_dir(
 
     yield test_dir
 
+    # Allure artifacts creation might involve the creation of `.tar.zst` archives,
+    # which aren't going to be used if Allure results collection is not enabled
+    # (i.e. --alluredir is not set).
+    # Skip `allure_attach_from_dir` in this case
+    if not request.config.getoption("--alluredir"):
+        return
+
     preserve_database_files = False
     for k, v in request.node.user_properties:
         # NB: the neon_env_builder fixture uses this fixture (test_output_dir).