ci: Temporarily pin to older nightly

There are a bunch of new lint errors that need to be addressed before we can
successfully build with latest nightly.

Author: nicholasbishop

.github/workflows/nightly_toolchain.toml

@@ -1,3 +1,3 @@
 [toolchain]
-channel = "nightly"
+channel = "nightly-2025-06-01"
 targets = ["aarch64-unknown-uefi", "i686-unknown-uefi", "x86_64-unknown-uefi"]

.github/workflows/rust.yml

@@ -187,7 +187,7 @@ jobs:
         run: cp .github/workflows/nightly_toolchain.toml rust-toolchain.toml
       - uses: Swatinem/rust-cache@v2
       - name: Build
-        run: cargo +nightly build --target x86_64-unknown-uefi --verbose -p uefi-std-example
+        run: cargo build --target x86_64-unknown-uefi --verbose -p uefi-std-example
   coverage:
     name: Test Coverage
     runs-on: ubuntu-latest