fix(embedded): Don't auto-discover build.rs files

With #12268, we moved the manifest root to be the scripts parent
directory, making it so auto-discovery might pick some things up.

We previously ensured `auto*` don't pick things up but missed `build.rs`
This is now addressed.

src/cargo/util/toml/embedded.rs

@@ -89,6 +89,9 @@ fn expand_manifest_(
         ));
         toml::Value::String(DEFAULT_EDITION.to_string())
     });
+    package
+        .entry("build".to_owned())
+        .or_insert_with(|| toml::Value::Boolean(false));
     package
         .entry("publish".to_owned())
         .or_insert_with(|| toml::Value::Boolean(DEFAULT_PUBLISH));
@@ -491,6 +494,7 @@ autobenches = false
 autobins = false
 autoexamples = false
 autotests = false
+build = false
 edition = "2021"
 name = "test-"
 publish = false
@@ -520,6 +524,7 @@ autobenches = false
 autobins = false
 autoexamples = false
 autotests = false
+build = false
 edition = "2021"
 name = "test-"
 publish = false

tests/testsuite/script.rs

@@ -523,11 +523,16 @@ fn main() {
 
     p.cargo("-Zscript script.rs --help")
         .masquerade_as_nightly_cargo(&["script"])
-        .with_status(101)
-        .with_stdout(r#""#)
-        .with_stderr_contains(
+        .with_stdout(
+            r#"Hello world!
+"#,
+        )
+        .with_stderr(
             "\
-[ERROR] could not compile `script` (build script) due to previous error
+[WARNING] `package.edition` is unspecifiead, defaulting to `2021`
+[COMPILING] script v0.0.0 ([ROOT]/foo)
+[FINISHED] dev [unoptimized + debuginfo] target(s) in [..]s
+[RUNNING] `[..]/debug/script[EXE] --help`
 ",
         )
         .run();