Fix typos: 'Bejing' to 'Beijing' in partition regress/docs - Mailing list pgsql-hackers

Hi hackers,

I noticed several occurrences of the misspelled city name 'Bejing' 
(should be 'Beijing') in our partition regressions and documentation. 
While these are just in test files and docs, I believe it's worth fixing.

Attached is the patch generated with git format-patch. After making the 
changes, I ran 'make checkworld' and verified all regression tests pass.

I'd appreciate any feedback on whether this aligns with our standards 
for such corrections.

Thanks,
JiaoShuntian