chore(ci): add clarification regarding test label (#7732)

Contributors use CI pipeline runs as a frame of reference to figure out
whether their work adhere's to Forgejo's quality assurance standards.
If a test label is missing and the CI does not run, the 'error message'
shown can cause confusion, as it might give the contributor the idea
that some action is expected from their part.

This change explicitly mentions that a reviewer must set the test
label.

Fixes forgejo/forgejo#7686.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7732
Reviewed-by: Beowulf <beowulf@beocode.eu>
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: Panagiotis "Ivory" Vasilopoulos <git@n0toose.net>
Co-committed-by: Panagiotis "Ivory" Vasilopoulos <git@n0toose.net>

.forgejo/workflows/merge-requirements.yml

@@ -31,7 +31,7 @@ jobs:
             || contains(toJSON(github.event.pull_request.labels), 'test/manual')
           )
         run: |
-          echo "Test label must be set to either 'present', 'not-needed' or 'manual'."
+          echo "A team member must set the label to either 'present', 'not-needed' or 'manual'."
           exit 1
       - name: Missing manual test instructions
         if: >