PGPRO-6828: fix tuplesort15.c due to changes in PostgreSQL 15

[MarinaPolyakova]

See the commits 27b77ecf9f4d5be211900eda54d8155ada50d696 and
94aa7cc5f707712f592885995a28e018c7c80488 in PostgreSQL 15.

[codecov]

Codecov Report

Merging #110 (cb41f78) into stable (d9cc86f) will increase coverage by 15.43%.
The diff coverage is 100.00%.

❗ Current head cb41f78 differs from pull request most recent head 10ede30. Consider uploading reports for the commit 10ede30 to get more accurate results

@@             Coverage Diff             @@
##           stable     #110       +/-   ##
===========================================
+ Coverage   38.54%   53.97%   +15.43%     
===========================================
  Files          33       30        -3     
  Lines       12370     8174     -4196     
===========================================
- Hits         4768     4412      -356     
+ Misses       7602     3762     -3840     

Impacted Files	Coverage Δ
src/rum.h	64.38% <ø> (-0.49%)	⬇️
src/rum_arr_utils.c	77.94% <ø> (-0.07%)	⬇️
src/rum_ts_utils.c	87.89% <ø> (-0.09%)	⬇️
src/rumbtree.c	60.85% <ø> (-3.50%)	⬇️
src/rumbulk.c	93.51% <ø> (ø)
src/rumdatapage.c	73.35% <ø> (-1.60%)	⬇️
src/rumentrypage.c	83.24% <ø> (-1.89%)	⬇️
src/rumget.c	87.62% <ø> (-0.50%)	⬇️
src/ruminsert.c	86.34% <ø> (-0.87%)	⬇️
src/rumscan.c	83.75% <ø> (-0.14%)	⬇️
... and 31 more

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