Delint existing shell scripts

ci/test-cuda.sh

@@ -1,17 +1,15 @@
 #!/bin/bash -e
 
-cd $(dirname $0)/..
+cd "$(dirname "$0")/.."
 
-if [[ -z "$libcuda_verify_ed25519_URL" ]]; then
-  echo libcuda_verify_ed25519_URL undefined
-  exit 1
-fi
+: "${libcuda_verify_ed25519_URL:?environment variable undefined}"
 
 export LD_LIBRARY_PATH=/usr/local/cuda/lib64
 export PATH=$PATH:/usr/local/cuda/bin
 curl -X GET -o libcuda_verify_ed25519.a "$libcuda_verify_ed25519_URL"
 
-source $HOME/.cargo/env
+# shellcheck disable=SC1090    # <-- shellcheck can't follow ~
+source ~/.cargo/env
 cargo test --features=cuda
 
 exit 0