Update CI so that warnings cause build failures.
Also fix a warning in `test-sanitizer-address`:
```
In function ‘strncpy’,
inlined from ‘clusterUpdateMyselfIp’ at cluster.c:545:13:
/usr/include/x86_64-linux-gnu/bits/string_fortified.h:106:10:
error: ‘__builtin_strncpy’ specified bound 46 equals destination size [-Werror=stringop-truncation]
106 | return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
```
980bb3ae19