Silence warnings when compiling pandas/_libs/parsers.pyx

[ShaharNaveh]

• closes #xxxx
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

This is getting rid of this warning:

pandas/_libs/parsers.c: In function ‘__pyx_f_6pandas_5_libs_7parsers_10TextReader__get_header’:
pandas/_libs/parsers.c:9313:27: warning: ‘__pyx_v_data_line’ may be used uninitialized in this function [-Wmaybe-uninitialized]
 9313 |   __pyx_t_5numpy_uint64_t __pyx_v_data_line;

[jbrockmendel]

Thanks @MomIsBestFriend

[jreback]

@jbrockmendel pls label and version PRs be fore merging