fix: set permissions of pages files — radicle-ci-broker

Temporary files have 0600 permissions, so they can’t be viewed via a web browser. Oops.

 use std::{
     fs::Permissions,
     io::Write,
     os::unix::fs::PermissionsExt,
     path::{Path, PathBuf},
     str::FromStr,
 };

         .map_err(|err| UtilError::CreateTemp(dirname.to_path_buf(), err))?;
     tmp.write_all(data)
         .map_err(|err| UtilError::WriteTemp(dirname.to_path_buf(), err))?;
     let mode = Permissions::from_mode(0o644);
     std::fs::set_permissions(tmp.path(), mode).map_err(UtilError::TempPerm)?;
     tmp.persist(filename)
         .map_err(|err| UtilError::RenameTemp(filename.to_path_buf(), err))?;
     Ok(())

     #[error("failed to write to temporary file in {0}")]
     WriteTemp(PathBuf, #[source] std::io::Error),
     #[error("failed to set permissions on temporary file")]
     TempPerm(#[source] std::io::Error),
     #[error("failed to rename temporary file to {0}")]
     RenameTemp(PathBuf, #[source] tempfile::PersistError),
 }