Fixes T9832. We currently refuse to recognize project hashtags in remarkup if they begin with a digit. This is motivated by attempting to not recognize them if they contain only digits.
I don't think we really gain anything by this. Although most #123 in text are probably not project references, the cost of doing a lookup for them is quite small, and some of them are.
In cases where users use #123 to refer to tasks in an external system, they can use a rule for that with higher precedence than this one or not give their projects conflicting hashtags.