fix(tvix/store): Immediately return an error when using sled on /

We already do this for redb and for sled in SledDirectoryService.

Change-Id: I34c7178257a6a04e9f12ed4037a4ef585d7b0d54
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12060
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
Autosubmit: Ilan Joselevich <personal@ilanjoselevich.com>

tvix/store/src/pathinfoservice/sled.rs

@@ -21,6 +21,12 @@ pub struct SledPathInfoService {
 
 impl SledPathInfoService {
     pub fn new<P: AsRef<Path>>(p: P) -> Result<Self, sled::Error> {
+        if p.as_ref() == Path::new("/") {
+            return Err(sled::Error::Unsupported(
+                "cowardly refusing to open / with sled".to_string(),
+            ));
+        }
+
         let config = sled::Config::default()
             .use_compression(false) // is a required parameter
             .path(p);