Put T-libs-api PRs under Libraries

Author: tmandry

src/main.rs

@@ -268,7 +268,7 @@ fn partition_prs<'a>(
     iter: impl IntoIterator<Item = &'a json::Value>,
 ) -> (String, String, String, String, String) {
     let (compat_notes, rest) = partition_by_tag(iter, &["C-future-compatibility"]);
-    let (libs, rest) = partition_by_tag(rest, &["T-libs"]);
+    let (libs, rest) = partition_by_tag(rest, &["T-libs", "T-libs-api"]);
     let (lang, rest) = partition_by_tag(rest, &["T-lang"]);
     let (compiler, rest) = partition_by_tag(rest, &["T-compiler"]);