Fix clippy lints for dice related to 1.79.0 toolchain update.

```
error: field `0` is never read
  --> packages/modules/Virtualization/guest/pvmfw/src/dice.rs:39:15
   |
39 |     CborError(ciborium::value::Error),
   |     --------- ^^^^^^^^^^^^^^^^^^^^^^
   |     |
   |     field in this variant
   |
   = note: `-D dead-code` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(dead_code)]`
help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
   |
39 |     CborError(()),
   |               ~~

error: field `0` is never read
  --> packages/modules/Virtualization/guest/pvmfw/src/dice.rs:41:15
   |
41 |     DiceError(diced_open_dice::DiceError),
   |     --------- ^^^^^^^^^^^^^^^^^^^^^^^^^^
   |     |
   |     field in this variant
   |
help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
   |
41 |     DiceError(()),
   |               ~~

```

Bug: http://b/346588808
Test: ./toolchain/android_rust/tools/test_compiler.py --target aosp_husky --all-rust --reuse-prebuilt
Change-Id: I0d9a7afdcc06cf3a50e1d2541014c4d7f8562c87
diff --git a/guest/pvmfw/src/dice.rs b/guest/pvmfw/src/dice.rs
index 8be73a4..470711f 100644
--- a/guest/pvmfw/src/dice.rs
+++ b/guest/pvmfw/src/dice.rs
@@ -36,8 +36,10 @@
 #[derive(Debug)]
 pub enum Error {
     /// Error in CBOR operations
+    #[allow(dead_code)]
     CborError(ciborium::value::Error),
     /// Error in DICE operations
+    #[allow(dead_code)]
     DiceError(diced_open_dice::DiceError),
 }