change rust version

.gitea/workflows/build.yaml

@@ -4,17 +4,20 @@ on: [push]
 
 jobs:
   build-iso:
-    name: Build ISO (nightly)
+    name: Build ISO (nightly-2025-04-27)
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
 
-      - name: Setup Rust (nightly)
+      - name: Setup Rust (1.88.0-nightly 2025-04-27)
         uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
-          toolchain: nightly
+          toolchain: nightly-2025-04-27
           override: true
 
+      - name: Verify rustc version
+        run: rustc -V
+
       - name: cargo check (nel_os_bootloader)
         working-directory: nel_os_bootloader
         run: cargo check