format env vars correctly in terraform plan

.github/workflows/_deploy_lambda.yml

@@ -83,14 +83,21 @@ jobs:
       - name: Terraform Plan
         working-directory: ${{ inputs.lambda_path }}
         run: |
+          ENV_VARS=""
+          if [ -n "${{ inputs.environment_vars }}" ]; then
+            # convert multi-line to JSON map: key=value -> "key"="value"
+            ENV_VARS=$(echo "${{ inputs.environment_vars }}" | \
+              awk -F= '{gsub(/"/,"\\\""); printf "\"%s\"=\"%s\",",$1,$2}' | \
+              sed 's/,$//') # remove trailing comma
+            ENV_VARS="-var='environment_vars={${ENV_VARS}}'"
+          fi
+
           terraform plan \
             -var="stage=${{ inputs.stage }}" \
             -var="lambda_name=${{ inputs.lambda_name }}" \
             -var="ecr_repo_url=${{ steps.repo.outputs.ecr_repo_url }}" \
             -var="image_digest=${{ inputs.image_digest }}" \
-            $(if [ -n "${{ inputs.environment_vars }}" ]; then
-                echo "-var=\"environment_vars=${{ inputs.environment_vars }}\""
-              fi) \
+            $ENV_VARS \
             -out=lambdaplan
 
       - name: Terraform Apply