The coverage report shows that some error cases were not being tested;
add test cases for them.
While at it, move some recently added ones to the test_decoding suite:
the preventative check added in 43649b6a53 now causes servers with
wal_level=minimal to error out earlier than before.
Author: Álvaro Herrera <alvherre@kurilemu.de>
Reviewed-by: Baji Shaik <baji.pgdev@gmail.com>
Discussion: https://postgr.es/m/ahiwD29RNfVT4tjQ@alvherre.pgsql
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