ci: Disable cross for i686 Windows, add multilib for i686 Linux for Nightly (#592)

Disables an unnecessary use of cross for i686 Windows, and add multilib for i686 Linux since apparently that's needed now.

.github/workflows/nightly.yml

@@ -68,7 +68,7 @@ jobs:
           - {
               os: "ubuntu-18.04",
               target: "i686-unknown-linux-gnu",
-              cross: true,
+              cross: false,
               strip: true,
             }
           - {
@@ -143,6 +143,13 @@ jobs:
           override: true
           target: ${{ matrix.triple.target }}
 
+      - name: Install gcc-multilib for (Linux i686)
+        if: matrix.triple.target == 'i686-unknown-linux-gnu' || matrix.triple.target == 'i686-unknown-linux-musl'
+        run: |
+          sudo dpkg --add-architecture i386
+          sudo apt update
+          sudo apt install gcc-multilib -y
+
       - uses: Swatinem/rust-cache@v1
         with:
           key: ${{ matrix.triple.target }}