`include()`'ing nonexistant file now gives misleading "can only hash files" error

[staticfloat]

If a package has an incorrect include(), it used to throw an error like this:

$ cat src/Example.jl | head
module Example
export hello, domath

include("this_is_nonexistant.jl")

"""
    hello(who::String)

Return "Hello, `who`".
"""
$ julia +1.9 --project -e 'using Example' 2>&1 | head -1
ERROR: LoadError: SystemError: opening file "/Users/sabae/.julia/dev/Example/src/this_is_nonexistant.jl": No such file or directory

Whereas:

$ julia +master --project -e 'using Example' 2>&1 | head -1
ERROR: LoadError: AssertionError: can only hash files

This appears to have changed as of f2df1b4

[staticfloat]

@fatteneder pinging you since you were the author of the linked commit.

[fatteneder]

This PR https://github.com/JuliaLang/julia/pull/51798/files already contains a fix.
If needed I can extract the fix into a separate PR. Let me know.

[fatteneder]

Although, that fix would now throw an error when including a non-existent directory, e.g.

julia> include("/asdf")
ERROR: IOError: readdir("/asdf"): no such file or directory (ENOENT)

Previously, one could just include non-existent directories and julia would not do anything.
I guess this behavior should be preserved.
My bad, got confused, a non-existing directory is just a non-existing file and so the same error should be thrown.

[staticfloat]

Okay, sounds good! I am content to wait until that PR is merged!