Improve CI coredump detection

[svenklemm]

Occasionally tests would segfault but the coredump would not be
uploaded as artefact because the coredump was still in progress.
This patch changes CI to wait for potential in progress coredumps
to upload coredumps more reliably.

[codecov]

Codecov Report

Merging #2862 (6aec096) into master (b1dc030) will increase coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2862      +/-   ##
==========================================
+ Coverage   90.08%   90.19%   +0.11%     
==========================================
  Files         212      212              
  Lines       34772    34722      -50     
==========================================
- Hits        31324    31318       -6     
+ Misses       3448     3404      -44     

Impacted Files	Coverage Δ
src/chunk_append/planner.c	93.44% <100.00%> (ø)
src/loader/bgw_message_queue.c	84.51% <0.00%> (-3.23%)	⬇️
tsl/src/data_node_dispatch.c	97.02% <0.00%> (-0.25%)	⬇️
src/import/planner.c	70.30% <0.00%> (+11.12%)	⬆️

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[mkindahl]

The best would be if there is any way to check that a coredump is expected (e.g., checking the signal of the crashed pid), but there seems to be no easy way to do this. My worry is that 10 seconds is not enough, but at least this will improve the situation, so approving.