Update Rust crate indexmap to v2.8.0 (#16787)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [indexmap](https://redirect.github.com/indexmap-rs/indexmap) |
workspace.dependencies | minor | `2.7.1` -> `2.8.0` |

---

> [!WARNING]
> Some dependencies could not be looked up. Check the Dependency
Dashboard for more information.

---

### Release Notes

<details>
<summary>indexmap-rs/indexmap (indexmap)</summary>

###
[`v2.8.0`](https://redirect.github.com/indexmap-rs/indexmap/blob/HEAD/RELEASES.md#280-2025-03-10)

[Compare
Source](https://redirect.github.com/indexmap-rs/indexmap/compare/2.7.1...2.8.0)

- Added `indexmap_with_default!` and `indexset_with_default!` to be used
with
    alternative hashers, especially when using the crate without `std`.
-   Implemented `PartialEq` between each `Slice` and `[]`/arrays.
-   Removed the internal `rustc-rayon` feature and dependency.

</details>

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Cargo.lock

@@ -1362,9 +1362,9 @@ dependencies = [
 
 [[package]]
 name = "indexmap"
-version = "2.7.1"
+version = "2.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8c9c992b02b5b4c94ea26e32fe5bccb7aa7d9f390ab5c1221ff895bc7ea8b652"
+checksum = "3954d50fe15b02142bf25d3b8bdadb634ec3948f103d04ffe3031bc8fe9d7058"
 dependencies = [
  "equivalent",
  "hashbrown 0.15.2",