Fix failing test fallout from chapel-lang#19788

This test is only run on linux32, so escaped my testing and refers to
an internal module, which is no longer available by default.  Here,
I'm using an explicit `use` to bring the module's name into scope,
though this will also break if/when we implement the proposal in

---
Signed-off-by: Brad Chamberlain <bradcray@users.noreply.github.com>

test/execflags/thomasvandoren/exceedMemInts.chpl

@@ -1,3 +1,4 @@
+use MemTracking;
 writeln(max(uint(64)));
 writeln("memMax = ", MemTracking.memMax);
 writeln("memThreshold = ", MemTracking.memThreshold);