[libcxx] [test] D27023: Fix MSVC warning C4389 "signed/unsigned mismatch", part 10/12.

Add static_cast<int>. In these cases, the values are guaranteed to be small-ish,
and they're being compared to int elements.

test/std/containers/sequences/deque/deque.capacity/access.pass.cpp
Use int instead of unsigned to iterate from 0 to 10.

llvm-svn: 288747