Pin nightly due to miri issue (#19253)

# Objective

The required miri check is currently failing due to rust-lang/miri#4323
Let's pin nightly to yesterday to not be blocked today.

## Solution

- Pinned nightly to `nightly-2025-05-16`

## Testing

- Let's see if the pipeline is green on this PR :D

Author: NiklasEi

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ env:
   CARGO_PROFILE_TEST_DEBUG: 0
   CARGO_PROFILE_DEV_DEBUG: 0
   # If nightly is breaking CI, modify this variable to target a specific nightly version.
-  NIGHTLY_TOOLCHAIN: nightly
+  NIGHTLY_TOOLCHAIN: nightly-2025-05-16 # pinned until a fix for https://github.com/rust-lang/miri/issues/4323 is released
   RUSTFLAGS: "-D warnings"
   BINSTALL_VERSION: "v1.12.3"