Currently, if branchNameStrict is set to true, the documentation
indicates that it should get rid of all special characters in the branch
name. This appears to be the intended behavior, looking at the discussions
behind the addition of this feature.
However, in reality, if you have something like additionalBranchPrefix
set to {{packageFileDir}}-. this will add slashes to the branch name
which are not removed by the branchNameStrict option; you'll end up
with a branch like renovate/modules/foo-package-2-x.
Optimally, branchNameStrict being set to true would remove all
special characters from the branches. At the very least, there should be
clearly documented way to have branch names contain only alphanumeric
and hyphen characters. If, as the discussion in the issue indicates, it
would be a problem for the branchPrefix to be altered by the
branchNameStrict parameter, then it should be clearly explained in
the documentation that in order to get rid of all special characters,
you must both set branchNameStrict (or accept the current true
default value) and set branchPrefix to something not containing
any special characters.