Use more appropriate run key configuration for poetry:install task

The "Task" task runner tool is used to perform common development operations for the project.

Tasks may call other tasks. Under certain conditions, this can result in the same task being called redundantly. This
can be avoided by using the `run` key to configure the task so that redundant calls will be skipped.

Previously, the `poetry:install` task's `run` key was set to `once`, which causes all but the first call will be
skipped. A safer configuration is `when_changed`, which will skip subsequent calls, unless the task configuration has
changed.

Author: per1234

Taskfile.yml

@@ -425,7 +425,7 @@ tasks:
   # Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/assets/poetry-task/Taskfile.yml
   poetry:install:
     desc: Install Poetry
-    run: once
+    run: when_changed
     cmds:
       - |
         if ! which pipx &>/dev/null; then