This is the longest test in our suite, try to help CI a bit.
Before:
```
$ go test -run=TestGenerateAlphabet -count=10 .
ok git.frostfs.info/TrueCloudLab/frostfs-node/cmd/frostfs-adm/internal/modules/morph/generate 45.400s
```
After:
```
$ go test -run=TestGenerateAlphabet -count=10 .
ok git.frostfs.info/TrueCloudLab/frostfs-node/cmd/frostfs-adm/internal/modules/morph/generate 33.267s
```
Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
