ci: double number of worker for the day

Increase the number of works to help PR throughput as we get
close to code freeze.  Will revert this back after code freeze.

Signed-off-by: Kumar Gala <[email protected]>

Author: galak

.buildkite/pipeline.yml

@@ -4,7 +4,7 @@ steps:
     env:
       ZEPHYR_TOOLCHAIN_VARIANT: "zephyr"
       ZEPHYR_SDK_INSTALL_DIR: "/opt/toolchains/zephyr-sdk-0.12.4"
-    parallelism: 20
+    parallelism: 40
     timeout_in_minutes: 180
     retry:
       manual: true