Use fixed Nitghtly version for rustdocs and add CI config comments

.github/workflows/workspace.yml

@@ -19,6 +19,10 @@ jobs:
     - uses: actions/checkout@v3
     - uses: dtolnay/rust-toolchain@master
       with:
+        # We need Nightly for -Zbuild-std.
+        # Fixed Nigthly version is used to prevent
+        # CI failures which are not relevant to PR changes
+        # on introduction of new Clippy lints.
         toolchain: nightly-2024-06-11
         components: clippy,rust-src
     - name: std feature
@@ -79,7 +83,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: dtolnay/rust-toolchain@nightly # Needed for doc_auto_cfg
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          # We need Nightly for doc_auto_cfg
+          toolchain: nightly-2024-06-11
       - uses: Swatinem/rust-cache@v2
       - name: Generate Docs
         env: