ci: run style tests in parallel

While it's about 25% faster, it is not a big improvement in absolute
term, just 8s. But it is cheap and it's good to get feedback a bit
quicker.

before: 13 passed in 33.06s
after: 13 passed in 25.21s

Signed-off-by: Pablo Barbáchano <pablob@amazon.com>

.buildkite/pipeline_pr.py

@@ -22,7 +22,7 @@
 args = COMMON_PARSER.parse_args()
 
 step_style = {
-    "command": "./tools/devtool -y test -- ../tests/integration_tests/style/",
+    "command": "./tools/devtool -y test -- -n 8 --dist worksteal ../tests/integration_tests/style/",
     "label": "🪶 Style",
     "priority": DEFAULT_PRIORITY,
 }