std.Io.Uring: handle ReadOnlyFileSystem in dirOpenDir and dirRealPathFile

f4eecf8d7d added ROFS handling to openat but missed these two read-only
callers, breaking compilation of any Io.Evented program.

lib/std/Io/Uring.zig

@@ -2739,6 +2739,7 @@ fn dirOpenDir(
             error.FileBusy => return errnoBug(.TXTBSY),
             error.PathAlreadyExists => return errnoBug(.EXIST), // Not creating.
             error.OperationUnsupported => return errnoBug(.OPNOTSUPP), // No TMPFILE, no locks.
+            error.ReadOnlyFileSystem => return errnoBug(.ROFS), // Not creating.
             else => |e| return e,
         },
     };
@@ -3164,6 +3165,7 @@ fn dirRealPathFile(
     }, 0) catch |err| switch (err) {
         error.WouldBlock => return errnoBug(.AGAIN),
         error.OperationUnsupported => return errnoBug(.OPNOTSUPP), // Not asking for locks.
+        error.ReadOnlyFileSystem => return errnoBug(.ROFS), // Not creating.
         else => |e| return e,
     };
     defer ev.closeAsync(fd);