allocator-test: test_revoke take heap size

This test wants to ensure that it cycles the heap, but it doesn't need
to allocate huge objects to do so in all cases.  Scale the size of the
objects used with the total heap.

tests/allocator-test.cc

diff --git a/tests/allocator-test.cc b/tests/allocator-test.cc
index 685fc22..9abbc7e 100644
--- a/tests/allocator-test.cc
+++ b/tests/allocator-test.cc
@@ -39,7 +39,6 @@
 
 	Timeout noWait{0};
 
-	constexpr size_t AllocSize     = 0xff0;
 	constexpr size_t MaxAllocCount = 16;
 	constexpr size_t TestIterations =
 #ifdef NDEBUG
@@ -88,8 +87,11 @@
 	 * to the end of the function and, if this is inlined, ends up with some
 	 * branches that are more than 2 KiB away from their targets.
 	 */
-	__noinline void test_revoke()
+	__noinline void test_revoke(const size_t HeapSize)
 	{
+		const size_t AllocSize = HeapSize / (MaxAllocCount + 2);
+		debug_log("test_revoke using {}-byte objects", AllocSize);
+
 		allocations.resize(MaxAllocCount);
 		for (size_t i = 0; i < TestIterations; ++i)
 		{
@@ -745,7 +747,7 @@
 
 	test_blocking_allocator(HeapSize);
 	TEST_EQUAL(heap_quarantine_empty(), 0, "Could not flush quarantine");
-	test_revoke();
+	test_revoke(HeapSize);
 	test_fuzz();
 	allocations.clear();
 	allocations.shrink_to_fit();