[libc++] Fix ranges_rotate.pass.cpp complexity checks (#158144)

The complexity is "at most N swaps" _for each invocation of `rotate`_,
but the tests currently assert that the total number of swaps for N
calls is at most N. The standard allows that to be N squared, so the
test is either requiring more than the standard (and the comment in the
test) promises, or somebody just forgot to reset the counter on each
iteration.

Author: jwakely

libcxx/test/std/algorithms/alg.modifying.operations/alg.rotate/ranges_rotate.pass.cpp

@@ -173,6 +173,7 @@ constexpr bool test() {
       auto end   = adl::Iterator::TrackSwaps(in.data() + in.size(), swaps);
 
       for (std::size_t mid = 0; mid != input.size(); ++mid) {
+        swaps = 0;
         std::ranges::rotate(begin, begin + mid, end);
         assert(swaps <= expected);
       }
@@ -186,6 +187,7 @@ constexpr bool test() {
       auto range = std::ranges::subrange(begin, end);
 
       for (std::size_t mid = 0; mid != input.size(); ++mid) {
+        swaps = 0;
         std::ranges::rotate(range, begin + mid);
         assert(swaps <= expected);
       }