Collisions for the entire hash are rare, but this is just a prefix of the hash. I imagine it is significantly more common for a collision in the prefix.
I maintain a library that talks to the Have I Been Pwned password database, which uses a 5-hexadecimal-digit prefix of the SHA1 hash.
Someone filed a PR asking to add a cache for HIBP's responses, and I did some quick math and came up with ~1200 as a birthday-paradox number for the first five digits of a SHA1 hex digest (assuming uniform/random distribution of hex digits).