fix(ci): use Rustc nightly to build stablized naked functions

Rustc nightly version `rustc 1.88.0-nightly (d6c1e454a 2025-04-21)`.

Signed-off-by: Zhouqi Jiang <luojia@hust.edu.cn>

.github/workflows/Library.yml

@@ -157,7 +157,7 @@ jobs:
           - riscv64imac-unknown-none-elf
           - riscv32imac-unknown-none-elf
         TOOLCHAIN:
-          - nightly-2025-04-21
+          - nightly-2025-04-22
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4

README.md

@@ -20,8 +20,8 @@ or consult vendors if they provide discrete RustSBI package support.
 
 ## Minimum supported Rust version
 
-To compile RustSBI library, you need at least nightly Rust version of `rustc 1.83.0 (6b6a867ae 2024-11-27)`.
-We are going to target stable Rustc once 2024 edition is landed (on 2025-02-20).
+To compile RustSBI library, you need at least nightly Rust version of `rustc 1.88.0-nightly (d6c1e454a 2025-04-21)`.
+We are going to target stable Rustc once version 1.88.0 is landed (on 2025-06-25).
 
 ## Build this project