Change bgw_main field length to BGW_MAXLEN

[jnidzwetzki]

The content of bgw_main is copied into BackgroundWorker.bgw_function_name, which has a length of BGW_MAXLEN. This patch ensures that the size of these fields has the same length.

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Found by: #5340
Disable-check: force-changelog-changed

[codecov]

Codecov Report

Merging #5345 (289a67c) into main (0963609) will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #5345      +/-   ##
==========================================
+ Coverage   90.71%   90.76%   +0.05%     
==========================================
  Files         225      225              
  Lines       52014    44965    -7049     
==========================================
- Hits        47183    40812    -6371     
+ Misses       4831     4153     -678     

Impacted Files	Coverage Δ
src/bgw/scheduler.c	85.99% <100.00%> (-2.50%)	⬇️
tsl/src/nodes/frozen_chunk_dml/frozen_chunk_dml.c	0.00% <0.00%> (-84.45%)	⬇️
tsl/test/src/test_chunk_stats.c	42.85% <0.00%> (-49.74%)	⬇️
tsl/src/nodes/compress_dml/compress_dml.c	86.66% <0.00%> (-11.16%)	⬇️
src/chunk.c	89.18% <0.00%> (-4.57%)	⬇️
src/bgw_policy/chunk_stats.c	81.53% <0.00%> (-4.01%)	⬇️
tsl/test/src/remote/dist_commands.c	90.62% <0.00%> (-3.97%)	⬇️
tsl/src/partialize_finalize.c	92.03% <0.00%> (-3.91%)	⬇️
tsl/src/chunk.c	90.69% <0.00%> (-3.70%)	⬇️
src/nodes/chunk_append/transform.c	96.42% <0.00%> (-3.58%)	⬇️
... and 193 more

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