ci: add permissions for benchmark action

[github-actions[bot]]

Read:

+--------------------------------------------+----------+---------+
|                                            | tonbo    | rocksdb |
+=================================================================+
| random range reads                         | 121474ms | 37835ms |
|--------------------------------------------+----------+---------|
| random range reads                         | 119423ms | 37774ms |
|--------------------------------------------+----------+---------|
| random range projection reads              | 50360ms  | 38068ms |
|--------------------------------------------+----------+---------|
| random range projection reads              | 49150ms  | 38004ms |
|--------------------------------------------+----------+---------|
| random range projection reads (4 threads)  | 38993ms  | 38302ms |
|--------------------------------------------+----------+---------|
| random range projection reads (8 threads)  | 37406ms  | 37839ms |
|--------------------------------------------+----------+---------|
| random range projection reads (16 threads) | 35521ms  | 36297ms |
|--------------------------------------------+----------+---------|
| random range projection reads (32 threads) | 32821ms  | 36364ms |
+--------------------------------------------+----------+---------+

[github-actions[bot]]

Write:

+-------------------------------+--------+---------+
|                               | tonbo  | rocksdb |
+==================================================+
| bulk load                     | 6347ms | 9419ms  |
|-------------------------------+--------+---------|
| individual writes             | 8310ms | 10461ms |
|-------------------------------+--------+---------|
| individual writes (4 threads) | 8067ms | 10471ms |
|-------------------------------+--------+---------|
| individual writes (8 threads) | 7786ms | 10464ms |
|-------------------------------+--------+---------|
| batch writes                  | 7950ms | 7168ms  |
|-------------------------------+--------+---------|
| batch writes (4 threads)      | 7503ms | 7097ms  |
|-------------------------------+--------+---------|
| batch writes (8 threads)      | 7335ms | 7123ms  |
|-------------------------------+--------+---------|
| removals                      | 3092ms | 3801ms  |
+-------------------------------+--------+---------+