fix(update): Don't bother listing pre-release

There might be casses where we want to show pre-release as this grows
but, for now, there isn't too often a case where an update is held back,
you are on a pre-release, your pre-release is updating, and you want a pre-release.

Author: epage

src/cargo/ops/cargo_generate_lockfile.rs

@@ -184,6 +184,7 @@ pub fn update_lockfile(ws: &Workspace<'_>, opts: &UpdateOptions<'_>) -> CargoRes
             possibilities
                 .iter()
                 .map(|s| s.as_summary())
+                .filter(|s| s.version().pre.is_empty())
                 .map(|s| s.version().clone())
                 .max()
                 .filter(|v| added.version() < v)

tests/testsuite/update.rs

@@ -1500,7 +1500,7 @@ fn report_behind() {
         .with_stderr(
             "\
 [UPDATING] `dummy-registry` index
-[UPDATING] breaking v0.1.0 -> v0.1.1 (latest: v0.2.1-alpha.0)
+[UPDATING] breaking v0.1.0 -> v0.1.1 (latest: v0.2.0)
 ",
         )
         .run();