try the cargo-c install step as rustls-ffi uses it

Just `cargo install cargo-c` downloads the internet...

Author: icing

.github/workflows/linux.yml

@@ -77,8 +77,13 @@ jobs:
         with:
           toolchain: ${{ matrix.rust }}
 
-      - name: Install cargo-c
-        run: cargo install cargo-c
+      - name: Install cargo-c (Ubuntu)
+        if: runner.os == 'Linux'
+        env:
+          LINK: https://github.com/lu-zero/cargo-c/releases/latest/download
+          CARGO_C_FILE: cargo-c-x86_64-unknown-linux-musl.tar.gz
+        run: |
+          curl -L $LINK/$CARGO_C_FILE | tar xz -C ~/.cargo/bin
 
       - name: 'checkout rustls-ffi'
         run: |