fix(ci): set shell to bash for Windows

GitHub workflows apparently default to pwsh (PowerShell Core)
on Windows, which didn't work for the shell script.

.github/workflows/test-rust.yaml

@@ -37,6 +37,7 @@ jobs:
         with:
           crate: cargo-insta
       - run: ./.github/set_version.sh
+        shell: bash
       - name: 💰 Cache
         uses: Swatinem/rust-cache@v2
         with: