Parallel tests publication and subscription might fail due to concurrent tuple update

Hello hackers,

A recent desman failure [1] with the following diagnostics:
# parallel group (2 tests):  subscription publication
not ok 157   + publication                              2251 ms
ok 158       + subscription                              415 ms

--- /home/fedora/17-desman/buildroot/REL_16_STABLE/pgsql.build/src/test/regress/expected/publication.out 2024-12-09
18:34:02.939762233 +0000
+++ /home/fedora/17-desman/buildroot/REL_16_STABLE/pgsql.build/src/test/regress/results/publication.out 2024-12-09
18:44:48.582958859 +0000
@@ -1193,23 +1193,29 @@
 ERROR:  permission denied for database regression
 SET ROLE regress_publication_user;
 GRANT CREATE ON DATABASE regression TO regress_publication_user2;
+ERROR:  tuple concurrently updated
 SET ROLE regress_publication_user2;
 SET client_min_messages = 'ERROR';
 CREATE PUBLICATION testpub2;  -- ok
+ERROR:  permission denied for database regression

and postmaster.log containing:
2024-12-09 18:44:46.753 UTC [1345157:903] pg_regress/publication STATEMENT:  CREATE PUBLICATION testpub2;
2024-12-09 18:44:46.753 UTC [1345158:287] pg_regress/subscription LOG:  statement: REVOKE CREATE ON DATABASE REGRESSION
FROM regress_subscription_user3;
2024-12-09 18:44:46.754 UTC [1345157:904] pg_regress/publication LOG:  statement: SET ROLE regress_publication_user;
2024-12-09 18:44:46.754 UTC [1345157:905] pg_regress/publication LOG:  statement: GRANT CREATE ON DATABASE regression TO
regress_publication_user2;
2024-12-09 18:44:46.754 UTC [1345157:906] pg_regress/publication ERROR:  tuple concurrently updated
2024-12-09 18:44:46.754 UTC [1345157:907] pg_regress/publication STATEMENT:  GRANT CREATE ON DATABASE regression TO
regress_publication_user2;

shows that the subscription and publication tests are not concurrent-safe,
because modifying the same pg_database entry might fail with the "tuple
concurrently updated" error.

I've managed to reproduce the error with:
sed -E "s/(REVOKE CREATE ON DATABASE REGRESSION FROM regress_subscription_user3;)/$(printf '\\1%.0s' {1..2000})/" -i.bak \
  src/test/regress/sql/subscription.sql src/test/regress/expected/subscription.out
sed -E "s/(GRANT CREATE ON DATABASE regression TO regress_publication_user2;)/$(printf '\\1%.0s' {1..1000})/" -i.bak \
  src/test/regress/sql/publication.sql src/test/regress/expected/publication.out
sed -E "s/(test: publication subscription$)/$(printf '\\1\\n%.0s' {1..10})/" -i.bak src/test/regress/parallel_schedule

This makes `make check` fail like below:
# parallel group (2 tests):  subscription publication
ok 170       + publication                               202 ms
ok 171       + subscription                              100 ms
# parallel group (2 tests):  subscription publication
ok 172       + publication                               198 ms
not ok 173   + subscription                              107 ms
# parallel group (2 tests):  subscription publication
ok 174       + publication                               204 ms
ok 175       + subscription                              100 ms

src/test/regress/regression.diffs contains:
+ERROR:  tuple concurrently updated

This issue is reproduced starting from commit c3afe8cf5 (dated 2023-03-30),
which added "REVOKE CREATE ON DATABASE REGRESSION ..." into the subscription
test.

[1] https://buildfarm.postgresql.org/cgi-bin/show_stage_log.pl?nm=desman&dt=2024-12-09%2018%3A33%3A49&stg=check

Best regards,
Alexander