fix: skip chmod-0o000 permission tests when running as root

CI runs the test suite as root inside an unmodified Docker base image
(data.forgejo.org/oci/node:20-bookworm), where chmod 0o000 doesn't
actually block reads — root bypasses Unix permission bits entirely.
The two new permission-based tests from the previous commit passed
locally (non-root) but failed in CI for exactly that reason. Skip them
under root via a raw geteuid() FFI check instead of asserting behavior
the OS isn't enforcing.

Verified with cargo build/test (34 passed)/clippy -D warnings/fmt --check.

src/documents.rs

@@ -237,11 +237,29 @@ mod tests {
         assert_eq!(documents[1].text, "scanned");
     }
 
+    /// Unix permission bits are meaningless to a root process — it can read
+    /// anything regardless of mode — so the two `chmod 0o000` tests below
+    /// would fail under a root-run CI container (e.g. an unmodified Docker
+    /// base image) despite the code being correct. Skip rather than assert
+    /// behavior the OS isn't actually enforcing.
+    #[cfg(unix)]
+    fn running_as_root() -> bool {
+        unsafe extern "C" {
+            fn geteuid() -> u32;
+        }
+        unsafe { geteuid() == 0 }
+    }
+
     #[cfg(unix)]
     #[test]
     fn collect_documents_skips_an_unreadable_file_inside_a_directory_but_keeps_the_rest() {
         use std::os::unix::fs::PermissionsExt;
 
+        if running_as_root() {
+            eprintln!("skipping: running as root, chmod 0o000 has no effect");
+            return;
+        }
+
         let dir = tempdir().unwrap();
         let readable = dir.path().join("readable.txt");
         let unreadable = dir.path().join("unreadable.txt");
@@ -263,6 +281,11 @@ mod tests {
     fn collect_documents_fails_outright_on_an_unreadable_directory() {
         use std::os::unix::fs::PermissionsExt;
 
+        if running_as_root() {
+            eprintln!("skipping: running as root, chmod 0o000 has no effect");
+            return;
+        }
+
         let dir = tempdir().unwrap();
         std::fs::set_permissions(dir.path(), std::fs::Permissions::from_mode(0o000)).unwrap();