Skip invalid database pg_upgrade test on obsolete servers
When testing pg_upgrade against an old server, ignore failures on the
check to upgrade invalid databases. This is necessary because old
servers don't know to raise the appropriate error of the database being
invalid.
This change causes no reduction in coverage, because such old versions
don't know to mark databases invalid when a drop is interrupted; but
testing against such old servers is useful in some circumstances.
Backpatch to 16, where it cherry-picks with minimal conflicts.
On 16, perltidy
20230309 chooses to change an unrelated line. I let it
do that because that's the version we document as preferred for that
branch, even though it would make other changes to many other files in
the tree.
Discussion: https://postgr.es/m/
202404181539.lh42llaesnv3@alvherre.pgsql