fix: reject non-digit characters in valid_cc_number()
#1820
| Job | Run time |
|---|---|
| 5m 20s | |
| 6m 25s | |
| 5m 26s | |
| 5m 27s | |
| 5m 9s | |
| 27m 47s |
valid_cc_number()
#1820
| Job | Run time |
|---|---|
| 5m 20s | |
| 6m 25s | |
| 5m 26s | |
| 5m 27s | |
| 5m 9s | |
| 27m 47s |