recipes: rust: Set SSL_CERT_FILE explicitly

Otherwise, rust recipe fails to download using curl:

+ python3 /mnt/redox/recipes/dev/rust/source/x.py install --config config.toml --jobs 32
downloading https://static.rust-lang.org/dist/2026-04-14/rust-std-beta-x86_64-unknown-linux-gnu.tar.xz
running: curl --progress-bar --retry-all-errors --location \
--speed-time 30 --speed-limit 10 --connect-timeout 30 \
--output /tmp/nix-shell.LcAteo/tmpuv1ls9sy --continue-at - \
--retry 3 --show-error --remote-time --fail \
https://static.rust-lang.org/dist/2026-04-14/rust-std-beta-x86_64-unknown-linux-gnu.tar.xz
curl: (60) SSL certificate OpenSSL verify result: unable to get local issuer certificate (20)
More details here: https://curl.se/docs/sslcerts.html

curl failed to verify the legitimacy of the server and therefore could not
establish a secure connection to it. To learn more about this situation and
how to fix it, please visit the webpage mentioned above.
Warning: Problem (retrying all errors). Retrying in 1 second. 3 retries left.
curl: (60) SSL certificate OpenSSL verify result: unable to get local issuer certificate (20)
More details here: https://curl.se/docs/sslcerts.html

recipes/dev/rust/recipe.toml

@@ -54,6 +54,7 @@ fi
 # Don't poison the stage1 compiler (host -> host)
 unset AR AS CC CXX LD LDFLAGS NM OBJCOPY OBJDUMP RANLIB READELF RUSTFLAGS CARGO_ENCODED_RUSTFLAGS STRIP
 
+SSL_CERT_FILE="/etc/ssl/certs/ca-certificates.crt" \
 python3 "${COOKBOOK_SOURCE}/x.py" install \
     --config config.toml \
     --jobs ${COOKBOOK_MAKE_JOBS}