fix: compile -Wunterminated-string-initialization

[steve-chavez]

Closes #10. This option is included by default on GCC 15 with -Wextra.

Not really a bug in the codebase as we don't use the null terminator, we use the exact size of the BOM string for appending it. See:

pg_csv/src/pg_csv.c

Line 69 in d452df8

if (state->options->bom) appendBinaryStringInfo(&state->accum_buf, BOM, sizeof(BOM));

This now changes compilation to always use GCC 15.

[coveralls]

Pull Request Test Coverage Report for Build 17623090584

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.099%

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Totals
Change from base Build 17591197101:	0.0%
Covered Lines:	110
Relevant Lines:	111

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