Advice please - Stage one absence meeting after handing in my notice

Hello,
First time on Reddit and needing some advice!
I am currently signed off by my GP for stress and MH and handed in my notice to terminate my employment by the end of this academic year. I happened to log on to my emails today to search for something and read an email from HR asking me to attend a stage 1 absence meeting for next week. Attached was the sickness policy stating I should expect to be contacted by my school throughout my sickness period and detailing the procedure that leads to the scheduled meeting. I have contacted my union and am awaiting a response but wanted to see if there was any advice I could get here before responding to a separate message from my Head about meeting for a chat and responding to the email from HR,
Thank you in advance!