This is a version of a Punctuation Shaker (warning: tvtropes). To quote that page:
One of the easiest ways to give an exotic or alien spin to words
intended to have originated from an exotic language is to sprinkle it
liberally with unexpected punctuation marks. [...] After the
apostrophe, the second most common punctuation mark is the
diaeresis/umlaut [...] Its use in fantasy was probably popularized by
J.R.R. Tolkien (like MANY fantasy devices), who used it a lot. (He
used acute and circumflex accents even more.)
In short, it's "just trying to look a little bit unusual".
A quick glance at the Wikipedia list of Star Wars and Legends Characters shows that apostrophes and accents are the most used alternative to "normal" letters.
That said, these are all diacritics, and they all serve orthographic purposes, so accents should not be considered separate from circumflexes. Granted one is less familiar to us as English speakers, but they are still in the same family. Obviously, some writer somewhere chose to shake things up by using a different diacritic.
In-universe, you can blame the fact that there are at least three ways of writing Galactic Basic, not all with the same number of characters. So switching between writing systems in the same language would introduce this diacritics to the names. Not to mention the fact that there are thousands of separate languages. So translating from those would also do the same thing.
High Galactic was a writing system that saw use during the Clone Wars and the Galactic Civil War. It was effectively English with Latin Characters.
Aurebesh was a writing system used to transcribe Galactic Basic
Outer Rim Basic was a 26-letter writing system that was used in the Outer Rim Territories to transcribe Galactic Basic, although it was originally created for another language
Pages from Ezra Bridger's private journal, handwritten in High Galactic
Aurebesh letters and punctuation
"Jho" in Outer Rim Basic