Package ecosystem output for gitsubmodules PRs is inconsistent with dependabot.yml

[BadMagic100]

In dependabot.yml, package-ecosystem for submodules is gitsubmodule. When output by this action, the result is just submodules. Since the package ecosystem is documented to be:

The package-ecosystem configuration that was used by dependabot for this updated Dependency.

The output should be made consistent with what is declared in the yml file.

Example workflow where this took place: https://github.com/hpackage/hpackage-rs/actions/runs/4902525037/jobs/8754565816