be more generous with mem::usage() expected peak

For some reason, this varies wildly, from 80 to 120 easily.
No flakiness please, I think previously, while there was a bug,
the memory usage was way higher than that, so it's still
a valid test to prevent regressions

Author: Byron

gix-config/tests/mem.rs

@@ -27,7 +27,7 @@ fn usage() {
         peak = ByteSize(ALLOCATOR.max_allocated() as u64),
     );
     assert!(
-        used < 80 * 1024 * 1024,
+        used < 200 * 1024 * 1024,
         "we should now start using more memory than anticipated, to keep mem-amplification low"
     );
 }