Auto merge of #10862 - Muscraft:workspace-selection-test, r=epage

Add a test for regressions in selecting the correct workspace root

This adds a test to check for regressions in selecting the correct workspace when there are nested workspaces.

#10846 solved a problem with nested workspace resolution that was caused by #10776. `@ehuss` [suggested](#10846 (comment)) that a test should be added to ensure that this issue does not pop up again.

I ensured that this worked by testing against commit before #10846. Sporadically I would get an error that was the same as described in #10846.
```
error: package `{path}/cargo/target/tmp/cit/t0/foo/sub/foo/Cargo.toml` is a member of the wrong workspace
expected: {path}/cargo/target/tmp/cit/t0/foo/sub/Cargo.toml
actual:   {path}/cargo/target/tmp/cit/t0/foo/Cargo.toml
```
I then tested it on the commit with the fix and the test passed every time.

---

While this does add a test to catch any regression I am worried that it will not catch it every time.  It was noted in #10846 that this error would sometimes happen but not every time, in my testing I found this to be true as well. Since this is caused by the `HashMap` order changing each run, switching to something ordered like `BTreeMap` **_should_** catch any regressions every run (if the implementation were to ever change). I'm not sure if this is necessary so I figured I would note the concern here.

tests/testsuite/workspaces.rs

@@ -2454,3 +2454,50 @@ fn virtual_primary_package_env_var() {
     p.cargo("clean").run();
     p.cargo("test -p foo").run();
 }
+
+#[cargo_test]
+fn ensure_correct_workspace_when_nested() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [workspace]
+
+                [project]
+                name = "bar"
+                version = "0.1.0"
+                authors = []
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .file(
+            "sub/Cargo.toml",
+            r#"
+                [workspace]
+                members = ["foo"]
+            "#,
+        )
+        .file(
+            "sub/foo/Cargo.toml",
+            r#"
+                [project]
+                name = "foo"
+                version = "0.1.0"
+                authors = []
+
+                [dependencies]
+                bar = { path = "../.."}
+            "#,
+        )
+        .file("sub/foo/src/main.rs", "fn main() {}");
+    let p = p.build();
+    p.cargo("tree")
+        .cwd("sub/foo")
+        .with_stdout(
+            "\
+foo v0.1.0 ([..]/foo/sub/foo)
+└── bar v0.1.0 ([..]/foo)\
+        ",
+        )
+        .run();
+}