BAH-5026 | Drop the weekly cron from the Semgrep workflow

[vishalkarmalkarthoughtworks]

Removes the schedule: trigger from .github/workflows/semgrep.yml. Two lines, no other change.

Why

GitHub disables a scheduled workflow in a public repo after 60 days with no repository activity. Two details matter:

1. The disable applies to the whole workflow, not just the cron. pull_request and push stop firing too, so Semgrep stops running on every PR.
2. GitHub never re-enables it. Activity resuming does not undo it.

This already happened to two repos from this rollout. semgrep.yml was in state disabled_inactivity on Bahmni/bahmni-api-test-automation and Bahmni/openmrs-module-bedmanagement, so Semgrep had stopped running on their PRs entirely. Both have been re-enabled, and they would trip again in another 60 dormant days with the cron still in place.

What is unaffected

• Scanning on every pull request, and on push to the default branch. This is where the coverage comes from.
• workflow_dispatch, so an on-demand full scan is still one click in the Actions tab.

Diff

 on:
   pull_request:
   push:
     branches: [main, master]
-  schedule:
-    - cron: '24 13 * * 1'
   workflow_dispatch:

Ticket: https://bahmni.atlassian.net/browse/BAH-5026