database/models/version: Adjust published_by field to be optional

When "Trusted Publishing" is used we can no longer associate the release with a specific crates.io user account. The column is already nullable since old releases did not track the information, so there are no changes needed on the database side.

Author: Turbo87

crates/crates_io_database/src/models/version.rs

@@ -90,7 +90,7 @@ pub struct NewVersion<'a> {
     license: Option<&'a str>,
     #[builder(default, name = "size")]
     crate_size: i32,
-    published_by: i32,
+    published_by: Option<i32>,
     checksum: &'a str,
     links: Option<&'a str>,
     rust_version: Option<&'a str>,