docs: improve doctests for complex number instances in math/base/special/csignumf
#20635
| Job | Run time |
|---|---|
| 1m 39s | |
| 1m 39s |
math/base/special/csignumf
#20635
| Job | Run time |
|---|---|
| 1m 39s | |
| 1m 39s |