Fix CI: toolchain order and rustflags

- Install nightly first, then stable, so stable is the default for clippy
- Set rustflags: "" to prevent -D warnings from breaking cargo build-sbf
  (Anchor macros emit unexpected_cfgs warnings for anchor-debug, etc.)

Author: ananas-block

.github/workflows/ci.yml

@@ -20,14 +20,15 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: actions-rust-lang/setup-rust-toolchain@v1
-        with:
-          toolchain: ${{ env.RUST_TOOLCHAIN }}
-          components: clippy
       - uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
           toolchain: nightly
           components: rustfmt
+          rustflags: ""
+      - uses: actions-rust-lang/setup-rust-toolchain@v1
+        with:
+          toolchain: ${{ env.RUST_TOOLCHAIN }}
+          components: clippy
       - uses: extractions/setup-just@v2
       - run: just lint
 
@@ -39,6 +40,7 @@ jobs:
       - uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
           toolchain: ${{ env.RUST_TOOLCHAIN }}
+          rustflags: ""
       - name: Cache Solana CLI tools
         uses: actions/cache@v4
         with: