"Wizard" can be used for males and females
Dumbledore uses the term "wizards" to refer to both males and females.
HERMIONE: Please believe us.
DUMBLEDORE: I do, Miss Granger.
But the word of three 13-year-old
wizards will convince few others
- Prisoner of Azkaban (film)
The shrunken heads also use "wizards" to refer to both males and females when Ron and Hermione try to follow Harry, who is under the invisibility cloak, into a tavern at Hogsmeade.
HERMIONE: Harry!
SHRUNKEN HEAD 1: No underage wizards allowed in today!
SHRUNKEN HEAD 2: Shut the [...] door!
HERMIONE: So rude.
RON: Thick heads.
- Prisoner of Azkaban (film)
Ron uses "wizard" to describe a group of presumably mixed gender individuals.
Harry -- this is a Pocket Sneakoscope. If there's someone untrustworthy around, it's supposed to light up and spin. Bill says it's rubbish sold for wizard tourists and isn't reliable, because it kept lighting up at dinner last night. But he didn't realize Fred and George had put beetles in his soup.
- Prisoner of Azkaban (book)
In all these situations the term "wizards" was used to describe a group of males and females. It is presumably acceptable to do so as it is unlikely that Dumbledore, a polite and respectable person, would use the wrong word.
That said, there are other terms that are also gender neutral, such as:
- "magician"
- "magical"
- "magic folk"
- "the wizarding world"
- "wand carrier"
More specific, but still gender neutral terms include:
- "aurors"
- "students"
- "hogwartians"
The term "wizarding" seems to be fairly common
From Prisoner of Azkaban (book):
- "the wizarding world"
- "wizarding village"
- "wizarding newspaper"
- "Gringotts Wizarding Bank"
"So Harry had had no word from any of his wizarding friends for five long weeks"