Dmitri Shostakovich (right) photographed with Yevgeny Mravinsky who conducted the Fifth Symphony’s premiere in 1937

It’s not so much the tempo, and they vary considerably, not least Kurt Masur’s massive strides (LPO label), but more the rallentando that most conductors make on the final few bars (Mark Wigglesworth on his BIS recording an exception), a stratagem that is, it must be said, perfectly plausible. However, I believe there is no such marking in the score (but I don’t know), so when a performance maintains the chosen speed throughout the ultimate coda it seems to me to be exactly right. Try, for example, Vladimir Fedoseyev & the Hiroshima Symphony Orchestra (audio of Finale; from a performance on December 10, 2020), as direct as can be:

(Following which there’s an encore, a movement from Tchaikovsky’s ‘Mozartiana’ Suite.)

Here’s Mravinsky as a reference, from 1973, Leningrad; slower anyway and with some broadening at the very end.