t/test_lib: avoid naked bash arrays in file_lineno
662f9cf154 (tests: when run in Bash, annotate test failures with file name/line number, 2020-04-11), introduces a way to report the location (file:lineno) of a failed test case by traversing the bash callstack. The implementation requires bash and uses shell arrays and is therefore protected by a guard but NetBSD sh will still have to parse the function and therefore will result in: ** t0000-basic.sh *** ./test-lib.sh: 681: Syntax error: Bad substitution Enclose the bash specific code inside an eval to avoid parsing errors in the same way than 5826b7b595 (test-lib: check Bash version for '-x' without using shell arrays, 2019-01-03) Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>