pgsql: Make sure to detach injection points for re-attaching

Make sure to detach injection points for re-attaching

The new test for enabling data checksums with concurrent CREATE
DATABASE calls use the same injection points as a previous test
but accidentally missed detaching the injection point first.

Fix by detaching the injection point in the PG_TEST_EXTRA SKIP
block to make it can be reused. Pointed out by buildfarm member
porpoise which failed with:

die: error running SQL: 'psql:<stdin>:1:
ERROR: injection point "datachecksumsworker-fake-temptable-wait"
already defined'

Backpatch to v19 where online checksums were introduced.

Author: Daniel Gustafsson <daniel(at)yesql(dot)se>
Reported-by: Buildfarm member porpoise
Reviewed-by: Jonathan Gonzalez V. <jonathan(dot)abdiel(at)gmail(dot)com>
Discussion: https://postgr.es/m/28CF6FD9-E1C4-4C04-8270-E3305AC46171@yesql.se
Backpatch-through: 19

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/ca7709f78f205d9e6685dee47b92dfadbc1b0ac7

Modified Files
--------------
src/test/modules/test_checksums/t/005_injection.pl | 3 +++
1 file changed, 3 insertions(+)