Copying the last byte was pointless, since the next line overwrites it,
and resulted in a compiler warning:
../src/intel/common/intel_measure.c: In function 'intel_measure_init':
../src/intel/common/intel_measure.c:68:7: warning: 'strncpy' specified bound 1024 equals destination size [-Wstringop-truncation]
68 | strncpy(env_copy, env, 1024);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
This allows dropping -Wno-error=stringop-truncation from the
debian-x86_64-asan & debian-{arm64,x86_64}-ubsan CI jobs.
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/39429>
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