Add weekly merge workflow and update CI triggers

[Arlodotexe]

This PR adds a weekly-merge.yml workflow file that merges main into rel/weekly on a chron schedule.

When this merge happens, our usual build.yml will be triggered and should diff with the merge from the week prior (the last push).

If no incremental changes are found by our build.yml, the build will exit early as usual.

[Copilot]

Pull Request Overview

This PR adds automated weekly merging functionality that merges the main branch into rel/weekly every Wednesday at 08:00 UTC. The build workflow is updated to trigger on pushes to the rel/weekly branch and when the weekly merge workflow completes, enabling continuous integration for the weekly release branch.

• Adds a scheduled workflow to automatically merge main into rel/weekly branch weekly
• Updates CI triggers to include the rel/weekly branch and workflow completion events
• Configures proper Git permissions and automated commit handling for the merge process

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
.github/workflows/weekly-merge.yml	New workflow file implementing the weekly merge automation with cron scheduling and manual trigger support
.github/workflows/build.yml	Updated CI triggers to include rel/weekly branch pushes and WeeklyMerge workflow completion events

Comments suppressed due to low confidence (1)

.github/workflows/weekly-merge.yml:1

• [nitpick] The workflow name 'WeeklyMerge' should follow GitHub Actions naming conventions with spaces or hyphens for better readability. Consider 'Weekly Merge' or 'weekly-merge'.

name: WeeklyMerge

[michael-hawker]

Think we need a couple of more bits.

[michael-hawker]

LGTM