ci: declare contents:read on test_old_cpu workflow

The test_old_cpu matrix runs Intel SDE-emulated tests on Sandy Bridge
and Haswell baselines. No GitHub API write. contents:read is the floor.

Style matches the per-job permissions block in build_wheels.yml
(id-token:write for trusted publishing) and the workflow-level shape
used by big_endian.yml, build_docs.yml, typecheck.yml.

Signed-off-by: Arpit Jain <arpitjain099@gmail.com>

Author: arpitjain099

.github/workflows/test_old_cpu.yml

@@ -11,6 +11,9 @@ on:
   pull_request:
   workflow_dispatch:
 
+permissions:
+  contents: read
+
 jobs:
   test_old_cpu:
     name: Test on ${{ matrix.cpu[1] }}