ci(template: Fix env var interpolation

Author: Techassi

template/.github/workflows/build.yaml.j2

@@ -84,7 +84,7 @@ jobs:
 
       - name: Install Rust ${{ env.RUST_TOOLCHAIN_VERSION }} toolchain
         shell: bash
-        run: rustup toolchain install "RUST_TOOLCHAIN_VERSION"
+        run: rustup toolchain install "${RUST_TOOLCHAIN_VERSION}"
 
       - name: Setup Rust Cache
         uses: Swatinem/rust-cache@98c8021b550208e191a6a3145459bfc9fb29c4c0 # v2.8.0
@@ -160,7 +160,7 @@ jobs:
 
       - name: Install Rust ${{ env.RUST_TOOLCHAIN_VERSION }} Toolchain
         shell: bash
-        run: rustup toolchain install "RUST_TOOLCHAIN_VERSION"
+        run: rustup toolchain install "${RUST_TOOLCHAIN_VERSION}"
 
       - name: Build Container Image
         id: build