pgsql: Update .abi-compliance-history for change to CreateStatistics().

Update .abi-compliance-history for change to CreateStatistics().

As noted in the commit message for 5e4fcbe531, the addition of a
second parameter to CreateStatistics() breaks ABI compatibility,
but we are unaware of any impacted third-party code.  This commit
updates .abi-compliance-history accordingly.

Backpatch-through: 14-18

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/ad5cc3ad8906123b34738e3697f31dacfffc15b7

Modified Files
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.abi-compliance-history | 8 ++++++++
1 file changed, 8 insertions(+)