Fix pr-checks/tsconfig.json for TS6

[mbg]

Follow-up to #3800. The pr-checks/tsconfig.json file also needed to be updated, which was missed there and is fixed here.

Risk assessment

For internal use only. Please select the risk level of this change:

• Low risk: Changes are fully under feature flags, or have been fully tested and validated in pre-production environments and are highly observable, or are documentation or test only.

Which use cases does this change impact?

Environments:

• Testing/None - This change does not impact any CodeQL workflows in production.

How did/will you validate this change?

• End-to-end tests - I am depending on PR checks (i.e. tests in pr-checks).

If something goes wrong after this change is released, what are the mitigation and rollback strategies?

• Development/testing only - This change cannot cause any failures in production.

How will you know if something goes wrong after this change is released?

• Other - Please provide details.

Are there any special considerations for merging or releasing this change?

• No special considerations - This change can be merged at any time.

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Consider adding a changelog entry for this change.
• Confirm the readme and docs have been updated if necessary.

[Copilot]

Pull request overview

Updates configuration files to keep pr-checks compatible with the TypeScript 6 upgrade (follow-up to #3800), and ensures Dependabot also tracks dependencies in pr-checks.

Changes:

• Override pr-checks/tsconfig.json to use module: "preserve" (aligned with TS6 + moduleResolution: bundler expectations inherited from the root config).
• Update Dependabot configuration to monitor both the root and pr-checks npm directories.

Show a summary per file

File	Description
pr-checks/tsconfig.json	Overrides module to "preserve" to avoid inheriting the root commonjs module setting under TS6.
.github/dependabot.yml	Expands npm update scope to include both / and /pr-checks.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 0

[henrymercer]

This makes sense. It might also be worth updating the root tsconfig so that we typecheck pr-checks/**.ts as part of npm run build.