Respect subdirectories when locating Git workspaces (#5944)

## Summary

We were discovering the workspace from the Git repository root, so
attempting to build any subdirectories would fail.

Closes https://github.com/astral-sh/uv/issues/5942.

## Test Plan

```
cargo run pip install \
	git+https://github.com/flyteorg/flytekit.git@master#subdirectory=plugins/flytekit-flyteinteractive
```

crates/uv-distribution/src/source/mod.rs

@@ -1249,11 +1249,17 @@ impl<'a, T: BuildContext> SourceDistributionBuilder<'a, T> {
                 .await
                 .map_err(Error::CacheWrite)?;
 
+            let path = if let Some(subdirectory) = resource.subdirectory {
+                Cow::Owned(fetch.path().join(subdirectory))
+            } else {
+                Cow::Borrowed(fetch.path())
+            };
+
             return Ok(ArchiveMetadata::from(
                 Metadata::from_workspace(
                     metadata,
-                    fetch.path(),
+                    &path,
-                    fetch.path(),
+                    &path,
                     self.build_context.sources(),
                     self.preview_mode,
                 )

crates/uv/tests/lock.rs

@@ -500,6 +500,92 @@ fn lock_sdist_git() -> Result<()> {
     Ok(())
 }
 
+/// Lock a Git requirement using PEP 508.
+#[test]
+#[cfg(feature = "git")]
+fn lock_sdist_git_subdirectory() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["example-pkg-a @ git+https://github.com/pypa/sample-namespace-packages.git@df7530eeb8fa0cb7dbb8ecb28363e8e36bfa2f45#subdirectory=pkg_resources/pkg_a"]
+        "#,
+    )?;
+
+    deterministic! { context =>
+        uv_snapshot!(context.filters(), context.lock(), @r###"
+                success: true
+                exit_code: 0
+                ----- stdout -----
+
+                ----- stderr -----
+                warning: `uv lock` is experimental and may change without warning
+                Resolved 2 packages in [TIME]
+                "###);
+
+        let lock = fs_err::read_to_string(context.temp_dir.join("uv.lock")).unwrap();
+
+        insta::with_settings!({
+            filters => context.filters(),
+        }, {
+            assert_snapshot!(
+                lock, @r###"
+            version = 1
+            requires-python = ">=3.12"
+
+            [options]
+            exclude-newer = "2024-03-25 00:00:00 UTC"
+
+            [[package]]
+            name = "example-pkg-a"
+            version = "1"
+            source = { git = "https://github.com/pypa/sample-namespace-packages.git?subdirectory=pkg_resources%2Fpkg_a&rev=df7530eeb8fa0cb7dbb8ecb28363e8e36bfa2f45#df7530eeb8fa0cb7dbb8ecb28363e8e36bfa2f45" }
+
+            [[package]]
+            name = "project"
+            version = "0.1.0"
+            source = { editable = "." }
+            dependencies = [
+                { name = "example-pkg-a" },
+            ]
+            "###
+            );
+        });
+    }
+
+    // Re-run with `--locked`.
+    uv_snapshot!(context.filters(), context.lock().arg("--locked"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: `uv lock` is experimental and may change without warning
+    Resolved 2 packages in [TIME]
+    "###);
+
+    // Install from the lockfile.
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: `uv sync` is experimental and may change without warning
+    Prepared 2 packages in [TIME]
+    Installed 2 packages in [TIME]
+     + example-pkg-a==1 (from git+https://github.com/pypa/sample-namespace-packages.git@df7530eeb8fa0cb7dbb8ecb28363e8e36bfa2f45#subdirectory=pkg_resources/pkg_a)
+     + project==0.1.0 (from file://[TEMP_DIR]/)
+    "###);
+
+    Ok(())
+}
+
 /// Lock a Git requirement using PEP 508.
 #[test]
 #[cfg(feature = "git")]