chore: Adjust unit test job runners to be hardcoded to 6 instead of 8, reducing I/O load and hopefully deflaking some tests

Author: jason-famedly

.github/workflows/famedly-tests.yml

@@ -234,10 +234,10 @@ jobs:
         # Normally, this Github runner has 4 cores(vCPUs) available to it.
         # Using only one trial test runner does not saturate the cpu. Rough experimentation in the past led to having 3
         # of these runners per core as optimal, but now coverage is required and there may be the need
-        # to scale back a little. This should be 8 trial test runners/jobs. Adding in
+        # to scale back a little. This should be 6 trial test runners/jobs. Adding in
         # --debug=core will display which measurement core is in use. For python 3.14+
         # this is educational.
-      - run: poetry run coverage run --debug=core -m twisted.trial -j$((`nproc` * 2 )) tests
+      - run: poetry run coverage run --debug=core -m twisted.trial -j6 tests
         env:
           SYNAPSE_POSTGRES: ${{ matrix.job.database == 'postgres' || '' }}
           SYNAPSE_POSTGRES_HOST: /var/run/postgresql