random-util: fix compilation error

random-util: fix compilation error

Fixes the following error:
```
../src/basic/random-util.c: In function "fallback_random_bytes":
../src/basic/random-util.c:45:26: error: initializer-string for array of "char" is too long [-Werror=unterminated-string-initialization]
   45 |                 .label = "systemd fallback random bytes v1",
      |                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
```