ENH Dispatch patch tag workflow instead of running directly

[GuySartorelli]

Dispatches the new workflow added in silverstripe/module-standardiser#66 instead of running patch tagging directly.

This removes the need for content:write permissions in ci.yml

Issue

• Error when using workflow: ”The nested job 'genmatrix' is requesting 'pull-requests: read'“ #137

[GuySartorelli]

Note that https://github.com/GuySartorelli/issue-template-playground/actions/runs/10153987547/job/28078370071 shows the workflow fails when the actions: write permission is missing, and https://github.com/GuySartorelli/issue-template-playground/actions/runs/10154036879/job/28078504318 shows it works when that permission is provided.

[GuySartorelli]

• With no permissions we get told we need pull-requests: read.
• After adding that, we get told we need contents:read
• With both permissions we have no permissions errors.

Ignore the fact that CI there is still red - that's just 'cause there's nothing for generate-matrix to output for that repo, and CI doesn't like having no matrix when it's told there will be one.

I also tested these permissions in a repo that actually does get a generated matrix and it works as expected, red job not-withstanding

[GuySartorelli]

Rebased so CI passes in my repo (needed the chromedriver fix)