You need to remove one space in:
[includeIf "gitdir: F:/Work/CompanyName/"]
i.e., make this read:
[includeIf "gitdir:F:/Work/CompanyName/"]
Note the lack of a blank between the colon after gitdir and the path name to be tested.
(Your Git also needs to be at least version 2.13. You might consider using gitdir/i:f:/work/companyname/ so that you are not case-sensitive here, assuming your host system is also not case-sensitive, as the F: part suggests. The final slash is important as well; don’t omit it without understanding what it does)