pgsql: Use Test::Builder::todo_start(), replacing $::TODO.

Use Test::Builder::todo_start(), replacing $::TODO.

Some pre-2017 Test::More versions need perfect $Test::Builder::Level
maintenance to find the variable.  Buildfarm member snapper reported an
overall failure that the file intended to hide via the TODO construct.
That trouble was reachable in v11 and v10.  For later branches, this
serves as defense in depth.  Back-patch to v10 (all supported versions).

Discussion: https://postgr.es/m/20220202055556.GB2745933@rfd.leadboat.com

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/3a32e53e1f383090f27b23d4356eb1d19172ef1b

Modified Files
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contrib/amcheck/t/003_cic_2pc.pl | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)