ERBB2 and aneurysmal bone cyst: Primary outcome analysis of the phase 3 SONIA trial (BOOG 2017‐03) on selecting the optimal schedule for the use of cyclin‐dependent kinases 4 and 6 (CDK4/6) inhibitors for patients with hormone receptor‐positive (HR+), HER2‐negative (HER2−) advanced breast cancer (ABC).