Change test data from 6.7 to 6.5

6.5 is an exact binary number (4 + 2 + 0.5), so all conversions to
string will result in "6.5", regardless of how many digits of precision
are used.

This is done in advance of changing QVariant to add more digits of
precision, which would cause toString() of 6.7 to result in
"6.7000000000000002".

Change-Id: I19ea4c5bb02b99f0655c0b9bc9dc09f06ec654e5
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>