batch installation should fall back to cargo install unless told --no-fallback

[alsuren]

in the step "Test batch installation with curl" of https://github.com/cargo-bins/cargo-quickinstall/actions/runs/11780483526/job/32811167615 I got:

+ cargo run -- --no-binstall cargo-quickinstall cargo-nextest@0.9.50
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.03s
     Running `target/debug/cargo-quickinstall --no-binstall cargo-quickinstall 'cargo-nextest@0.[9](https://github.com/cargo-bins/cargo-quickinstall/actions/runs/11780483526/job/32811167615#step:11:10).50'`
Error: Command failed:
    curl --user-agent "cargo-quickinstall/0.3.4 client (alsuren@gmail.com)" --location --silent --show-error --fail "https://github.com/cargo-bins/cargo-quickinstall/releases/download/cargo-quickinstall-0.3.4/cargo-quickinstall-0.3.4-aarch64-apple-darwin.tar.gz"
Stderr:
curl: (56) The requested URL returned error: 404

• If I don't specify --no-fallback, I would expect this to fall back to cargo install. This test should then be changed to specify --no-fallback

• This problem only shows up because we did a release and cargo-quickinstall hasn't built itself yet. I will think about fiddling with the release action to trigger a bunch of self-builds or something, to make this fail less often. In this case, I manually ran make recheck locally to trigger the builds and then re-ran my CI build. Hopefully fixed in trigger self build after every release #323