Fix missing reference action only work if package have been `using`d

[fredrikekre]

Probably an issue in SymbolServer or StaticLint, but e.g. in

import Example
hello("foo")              # Missing reference hello

this can't be fixed because Example isn't in

LanguageServer.jl/src/requests/actions.jl

Line 292 in 018d838

for m in values(tls.modules)

In contrast,

using Example
some_non_exported_function(..)

works.