Is it safe to drill small holes in load-bearing concrete beams for expansion bolts?
You can actually punch surprising large holes in the middle of a beam without diminishing its load-bearing capacity.  This is because that capacity is largely a function of only the top and bottom portions of the beam and how far apart they are.

Engineered floor joists are a good example of this:


It would take a structural engineer to tell you exactly how much the load-bearing capacity will be reduced, but I can tell you that this amount will be at least an order of magnitude less than the margin for error in manufacturing the beam.

Don't worry about it.  It's what these things are made for.