Silence pedantic compiler warning introduced in ce340e530d1

Silence pedantic compiler warning introduced in ce340e530d1

.../src/common/file_utils.c: In function ‘pg_pwrite_zeros’:
.../src/common/file_utils.c:543:9: warning: ‘static’ is not at beginning of declaration [-Wold-style-declaration]
  543 |         const static PGAlignedBlock zbuffer = {{0}};    /* worth BLCKSZ */