Does ablution become void when a man's finger accidentally touches a woman's finger?

Your ablution (wudu') is not invalidated by what you mentioned. The preponderant view among scholars is that mere touching does not invalidate ablution, based on what was narrated from Aisha (may Allah be pleased with her) "that the Prophet (peace and blessings of Allah be upon him) kissed some of his wives, then went out to prayer without performing ablution."