Deps: Update a8c ci toolkit to 3.4.2

Release Notes: https://github.com/Automattic/
a8c-ci-toolkit-buildkite-plugin/releases/tag/3.4.2

------------------------------------------------------------------------

FYI: The breaking change in '3.0.0' is due to removing the 'nvm_install'
command, but this repo doesn't use that anywhere anyway. As such, it is
safe to apply this update.

Author: ParaskP7

.buildkite/pipeline.yml

@@ -4,7 +4,7 @@
 common_params:
   # Common plugin settings to use with the `plugins` key.
   - &common_plugins
-    - automattic/a8c-ci-toolkit#2.15.0
+    - automattic/a8c-ci-toolkit#3.4.2
 
 agents:
   queue: "android"

.buildkite/schedules/dependency-analysis.yml

@@ -4,7 +4,7 @@
 common_params:
   # Common plugin settings to use with the `plugins` key.
   - &common_plugins
-    - automattic/a8c-ci-toolkit#2.15.0
+    - automattic/a8c-ci-toolkit#3.4.2
 
 agents:
   queue: "android"