BUG #17399: Dead tuple number stats not updated on long running queries

The following bug has been logged on the website:

Bug reference:      17399
Logged by:          Soni
Email address:      diptatapa@gmail.com
PostgreSQL version: 13.5
Operating system:   Red Hat Enterprise Linux release 8.5 (Ootpa)
Description:

Hello All,
I think I found a bug.

While there are long running queries, a vacuum that start and end during the
long running queries, the stats of pg_stat_user_tables.n_dead_tup not
updated. The real dead tuple on the table is cleaned up, but not the
stats.
So, if dead tuple percentage on pg_stat_user_tables is above
autovacuum_vacuum_scale_factor, then the autovacuum keeps triggered during
the long running queries.