Update URL of taskfile schema in "Check Taskfiles" workflow

The "Check Taskfiles" template workflow validates the project's taskfiles against the official JSON schema.

The contents of that schema was recently moved from the previous location in the Schema Store to the Task project
repository:

go-task/task#910

An attempt was made to mitigate the impact of that move by replacing the content in the original schema with an external
reference to the new one. However, the schema validator used by the workflow does not automatically follow external
references, which caused the workflow to fail:

schema /home/runner/work/_temp/taskfile-schema/taskfile.json is invalid
error: can't resolve reference https://taskfile.dev/schema.json from id #

Although this could be resolved by also downloading the referenced schema, since the original schema intentionally does
not contain anything of value, the better fix is to simply use the real schema directly in the workflow.

Author: per1234

.github/workflows/check-taskfiles.yml

@@ -66,8 +66,8 @@ jobs:
         id: download-schema
         uses: carlosperate/download-file-action@v2
         with:
-          # See: https://github.com/SchemaStore/schemastore/blob/master/src/schemas/json/taskfile.json
-          file-url: https://json.schemastore.org/taskfile.json
+          # Source: https://github.com/SchemaStore/schemastore/blob/master/src/schemas/json/taskfile.json
+          file-url: https://taskfile.dev/schema.json
           location: ${{ runner.temp }}/taskfile-schema
 
       - name: Install JSON schema validator