Pin old nightly to get back nightly rustdoc features

.github/workflows/docs.yml

@@ -21,12 +21,20 @@ jobs:
         uses: actions-rs/toolchain@v1
         with:
           profile: minimal
-          # Needed for use of unstable options
-          toolchain: nightly
+          # Nightly needed for use of unstable options
+          # Pinned because of https://github.com/rust-lang/cargo/issues/10744
+          toolchain: nightly-2022-03-01
           override: true
 
       - uses: Swatinem/rust-cache@v1
 
+      # lock_api 0.4.7 doesn't compile with our currently-pinned nightly
+      - name: Downgrade lock_api
+        uses: actions-rs/cargo@v1
+        with:
+          command: update
+          args: -p lock_api --precise 0.4.6
+
       - name: Build docs
         uses: actions-rs/cargo@v1
         with: