Fix locale-dependent test case.

Fix locale-dependent test case.

psql parses the interval argument of \watch with locale-dependent
strtod().  In commit 00beecfe8 I added a test case that exercises
a fractional interval, but I hard-coded 0.01 which doesn't work
in locales where the radix point isn't ".".  We don't want to
change this longstanding parsing behavior, so fix the test case
to generate a suitably locale-aware spelling.

Report and patch by Alexander Korotkov.

Discussion: https://postgr.es/m/CAPpHfdv+10Uk6FWjsh3+ju7kHYr76LaRXbYayXmrM7FBU-=Hgg@mail.gmail.com