Replace <sha>^ with the previous sha (or something more acceptable) in the diff editor title

[alexdima]

Testing #91329

When viewing the timeline for a file, and clicking on the item, the title looks like:

Two things stand out:

• there appears to be a unicode string encoding issue, where the unicode code point is escaped \u27f7
• the same commit sha is rendered twice, once with sha^ format, which is very technical and not user friendly IMHO. I recommend to try to render the sha only once.

[eamodio]

I've fixed the encoding problem, but will still need to address the previous sha (<sha>^) issue