Run Doc builds in CI

This ensures that the doc build will succeed when run later, since
rustdoc and rustc are known to have different ICEs.

Author: jyn514

collector/src/bin/rustc-perf-collector/main.rs

@@ -633,7 +633,7 @@ fn main_result() -> anyhow::Result<i32> {
                 &mut rt,
                 conn,
                 &ArtifactId::Commit(commit),
-                &[BuildKind::Check], // no Debug or Opt builds
+                &[BuildKind::Check, BuildKind::Doc], // no Debug or Opt builds
                 &RunKind::all(),
                 Compiler::from_sysroot(&sysroot),
                 &benchmarks,