`std.fs.accessAbsolute` asserts if the user proposed path is absolute,
which we are seemingly passing as-is with no validating that it is.
When running with safety checks on, passing non-absolute path to
--working-directory will make ghostty crash.
I changed it to use `Dir.access`, which is just `accessAbsolute` without
the check.
This has the side effect of also allowing relative working directory.
5bb05996eb