Add source URL comment to spell check assets

This will make it easier for the maintainers to sync fixes and improvements in either direction between the upstream
"template" assets and their installation in this repository.

Author: per1234

.github/workflows/spell-check-task.yml

@@ -1,3 +1,4 @@
+# Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/spell-check-task.md
 name: Spell Check
 
 # See: https://docs.github.com/en/free-pro-team@latest/actions/reference/events-that-trigger-workflows

Taskfile.yml

@@ -402,13 +402,15 @@ tasks:
     cmds:
       - npx prettier --write .
 
+  # Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/assets/spell-check-task/Taskfile.yml
   general:check-spelling:
     desc: Check for commonly misspelled words
     deps:
       - task: poetry:install-deps
     cmds:
       - poetry run codespell
 
+  # Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/assets/spell-check-task/Taskfile.yml
   general:correct-spelling:
     desc: Correct commonly misspelled words where possible
     deps: