The full warning message I get in the .log is
Package biblatex Warning: Conflicting options.
(biblatex) '<namepart>inits' conflicts with 'uniquename=full'.
(biblatex) Setting 'uniquename=init' on input line 10.
This tells you that since you only want given/first name initials with the option giveninits, you can't get full uniquename disambiguation if need be (as automatically requested by the authoryear style with uniquename=full). The message goes on to say that the option will be set to
uniquename=init
to allow for name disambiguation at least by name initials.
If you don't want the warning in the first place, just load biblatex with uniquename=init from the start.
\usepackage[backend=biber,style=authoryear,uniquename=init,giveninits]{biblatex}
If you don't want name disambiguation at all, use uniquename=false instead (see biblatex, authoryear style: In-text citations display first name initials for certain bibliography entries for example).