Avoid explicit loop when updating OrderedSet

[Illviljan]

Following recommendation from: #7824 (comment)

# main:
a = tuple(f"dim_{i}" for i in range(500))
%timeit OrderedSet(a)
46 µs ± 2.26 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)

# This PR:
a = tuple(f"dim_{i}" for i in range(500))
%timeit OrderedSet(a)
28.9 µs ± 476 ns per loop (mean ± std. dev. of 7 runs, 10000 loops each)

[mathause]

As we are 3.9+ I think we could now do

self._d =| dict.fromkeys(values)

but no need to update.