Add test for #6557 (#6558)

## What changed?
I realized it's easy to make a test for #6557 without direct access to
compare m.contents.

## Why?
prevent regressions

common/collection/sync_map_test.go

@@ -154,11 +154,16 @@ func TestMap_PopAll(t *testing.T) {
 	m.Set(4, 4)
 	m.Pop(4)
 
+	mCopy := m
+
 	values = m.PopAll()
 	assert.Equal(t, 3, len(values))
 	sum := 0
 	for _, v := range values {
 		sum += v
 	}
 	assert.Equal(t, 6, sum)
+
+	_, ok := mCopy.Get(3)
+	assert.False(t, ok, "SyncMap is not correctly copyable")
 }