Thread timestamp to tagging

This fixes a longstanding bug with GitHub tag signing where the
timestamp of the created tag would differ from the signature, causing
failed signature verification.

Author: Mark-Simulacrum

src/github.rs

@@ -147,6 +147,7 @@ impl RepositoryClient<'_> {
         struct CreateTagTaggerInternal<'a> {
             name: &'a str,
             email: &'a str,
+            date: String,
         }
 
         #[derive(serde::Deserialize)]
@@ -167,6 +168,8 @@ impl RepositoryClient<'_> {
             tagger: CreateTagTaggerInternal {
                 name: tag.tagger_name,
                 email: tag.tagger_email,
+                // ISO 8601 format
+                date: tag.timestamp.format("%Y-%m-%dT%H:%M:%S%Z").to_string(),
             },
         };
         let created = self
@@ -521,6 +524,7 @@ pub(crate) struct CreateTag<'a> {
     pub(crate) message: &'a str,
     pub(crate) tagger_name: &'a str,
     pub(crate) tagger_email: &'a str,
+    pub(crate) timestamp: chrono::DateTime<chrono::Utc>,
 }
 
 #[derive(serde::Deserialize)]

src/main.rs

@@ -835,7 +835,7 @@ impl Context {
         let tag_name = version.to_owned();
         let username = "rust-lang/promote-release";
         let email = "release-team@rust-lang.org";
-        let message = signer.git_signed_tag(
+        let (message, timestamp) = signer.git_signed_tag(
             commit,
             &tag_name,
             username,
@@ -846,10 +846,10 @@ impl Context {
         github.token(repository)?.tag(CreateTag {
             commit,
             tag_name: &tag_name,
-            // FIXME: we need to pass the timestamp too
-            message: &message.0,
+            message: &message,
             tagger_name: username,
             tagger_email: email,
+            timestamp,
         })?;
 
         Ok(())