DISCARD maps on deferred contexts do not seem to offer the same synchronization
guarantees as do DISCARD maps on the immediate context, at least not with
respect to subsequent NOOVERWRITE maps on the immediate context. This is not
particularly surprising, seeing as it is probably far more usual to only map a
resource on one kind of context or the other.

The test currently fails on Windows 11 on NVidia drivers, but it also fails on
Mesa, for what I think are the same reasons.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=52563
Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=54023