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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master

Details
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https://git.postgresql.org/pg/commitdiff/adbd00f7a59bcfbcd6907858499c94a27c6680ed

Modified Files
--------------
contrib/amcheck/t/003_cic_2pc.pl          | 3 ++-
src/test/recovery/t/027_stream_regress.pl | 4 ++--
2 files changed, 4 insertions(+), 3 deletions(-)