run_batch_script.yml: Fix grep checks by adding !

`grep` returns 0 if found, and 1 if not found. But we want the opposite: 1 if warning/error
is present, and 0 if there are no warnings/errors. So, we need to invert the output code.

I have no idea why these checks lasted as long as they did without this `!` inversion. The
`grep` commands only used options `-iF`, meaning (case-insensitive) and (non-regex
strings), so the options don't have anything to do with it.

Hopefully this will fix the erroneous failures?

.github/workflows/run_batch_script.yml

@@ -78,10 +78,10 @@ jobs:
       if: always()
       run: |
         cd "${{ github.event.repository.name }}/multi_subject/output/log"
-        # grep -iF "warning" process_data_sub-01.log
+        # ! grep -iF "warning" process_data_sub-01.log
 
     - name: Check results (errors in log)
       if: always()
       run: |
         cd "${{ github.event.repository.name }}/multi_subject/output/log"
-        grep -iF "error" process_data_sub-01.log
+        ! grep -iF "error" process_data_sub-01.log