envrc was using undefined variables (#94468)

Author: bukzor

.envrc

@@ -4,7 +4,7 @@
 # initialization (e.g. activating the venv) or giving recommendations on how to reach the desired state.
 # It also sets useful environment variables.
 # If you'd like to override or set any custom environment variables, this .envrc will read a .env file at the end.
-set -e
+set -eu
 
 # Upgrading Mac can uninstall the Command Line Tools, thus, removing our access to git
 # The message talks about xcrun, however, we can use the lack of git as a way to know that we need this
@@ -188,7 +188,7 @@ python3 -m tools.docker_memory_check
 if [ "${PWD##*/}" = "sentry" ]; then
     debug "Checking node..."
 
-    if [ "${SENTRY_DEVENV_SKIP_FRONTEND}" != "1" ]; then
+    if [ "${SENTRY_DEVENV_SKIP_FRONTEND:-}" != "1" ]; then
         if ! require node; then
             die "You don't seem to have node installed. Please run devenv sync."
         fi