Report all errors when taskfile schema validation occurs

The `ajv-cli` JSON schema validator is used to check the data format of the taskfile. The default behavior of `ajv-cli`
is to bail out on the first error.

I think it is slightly more convenient to get all the errors at once to allow fixing all of them in one go rather than
having to repeatedly run the validation before discovering all of them. This behavior is provided by adding the
`--all-errors` flag to the `ajv-cli`' commands.

Author: per1234

.github/workflows/check-taskfiles.yml

@@ -48,6 +48,7 @@ jobs:
         run: |
           # See: https://github.com/ajv-validator/ajv-cli#readme
           ajv validate \
+            --all-errors \
             --strict=false \
             -s "${{ steps.download-schema.outputs.file-path }}" \
             -d "${{ matrix.file }}"