pgsql: Fix upper limit for vacuum_cleanup_index_scale_factor

Fix upper limit for vacuum_cleanup_index_scale_factor

6ca33a88 sets upper limit for vacuum_cleanup_index_scale_factor to
DBL_MAX.  DBL_MAX appears to be platform-dependent. That causes
many buildfarm animals to fail, because we check boundaries of
vacuum_cleanup_index_scale_factor in regression tests.

This commit changes upper limit from DBL_MAX to just "large enough"
limit, which was arbitrary selected as 1e10.

Author: Alexander Korotkov
Reported-by: Tom Lane, Darafei Praliaskouski
Discussion: https://postgr.es/m/CAPpHfdvewmr4PcpRjrkstoNn1n2_6dL-iHRB21CCfZ0efZdBTg%40mail.gmail.com
Discussion: https://postgr.es/m/CAC8Q8tLYFOpKNaPS_E7V8KtPdE%3D_TnAn16t%3DA3LuL%3DXjfOO-BQ%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4d54543efa5eb074ead4d0fadb2af4161c943044

Modified Files
--------------
doc/src/sgml/config.sgml                  | 3 ++-
src/backend/access/common/reloptions.c    | 2 +-
src/backend/utils/misc/guc.c              | 2 +-
src/test/regress/expected/btree_index.out | 2 +-
4 files changed, 5 insertions(+), 4 deletions(-)