Add permissions to the Update Status Chart action

[StephanTLavavej]

Followup to #4223 where I said:

.github/workflows/update-status-chart.yml mentions github.token for the GraphQL API, but all it needs is public read-only access, so I don't think that it'll need to be changed.

Wrong! It autonomously commits changes:

STL/.github/workflows/update-status-chart.yml

Lines 31 to 37 in 1bc5ca6

	- name: Commit Changes
	run: |
	git config user.name "github-actions[bot]"
	git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
	git add src/daily_table.ts src/monthly_table.ts built/status_chart.mjs
	git diff-index --quiet HEAD || git commit -m "Automated update."
	git push origin gh-pages

So the workflow runs started failing with:

remote: Permission to microsoft/STL.git denied to github-actions[bot].
fatal: unable to access 'https://github.com/microsoft/STL/': The requested URL returned error: 403
Error: Process completed with exit code 128.

I've verified in my fork that granting the contents: write permission is sufficient - we don't need to grant issues: read and pull-requests: read.

[StephanTLavavej]

I'm speculatively mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.