Update bench

[Borber]

I noticed that https://tantivy-search.github.io/bench/ is still using version 0.16, while the latest version has come to 0.19.2, which should have a lot of performance improvements. But I don't know how much of an improvement.

As well, maybe automatic bench testing after each release would allow us to see the tantivy improvements more visually

[arifd]

I just checked the link and the version appears to be tantivy-0.20

[fulmicoton]

ah yes. I updated a few weeks ago.

[fulmicoton]

As well, maybe automatic bench testing after each release would allow us to see the tantivy improvements more visually

Keeing open for this