(docs) Remove errant comma from PR template

[denniskigen]

Requirements

• This PR has a title that briefly describes the work done, including the ticket number if there is a ticket.
• My work conforms to the OpenMRS 3.0 Styleguide.
• My work includes tests, or is validated by existing tests.

Related Issue

openmrs/openmrs-esm-core#339

[github-actions]

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Error: Error while trying to collect info after merging pr-template into master.

Error: Command failed: git merge FETCH_HEAD --allow-unrelated-histories

    at ChildProcess.exithandler (node:child_process:397:12)
    at ChildProcess.emit (node:events:394:28)
    at maybeClose (node:internal/child_process:1067:16)
    at Process.ChildProcess._handle.onexit (node:internal/child_process:301:5)

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_{Generated by @jsenv/file-size-impact during Report bundle size#1914977530 on d2a7994}