You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: multienv_step_runner.go
    path of file: ./repos/atlantis/server/core/runtime
    
    the code of the file until where you have to start completion: package runtime

import (
	"errors"
	"fmt"
	"strings"

	"github.com/runatlantis/atlantis/server/core/config/valid"
	"github.com/runatlantis/atlantis/server/events/command"
)

// EnvStepRunner set environment variables.
type MultiE
    
func (r *MultiEnvStepRunner) Run(ctx command.ProjectContext, command string, path string, envs map[string]string) (string, error) {
	res, err := r.RunStepRunner.Run(ctx, command, path, envs, false, valid.PostProcessRunOutputShow)
	if err != nil {
		return "", err
	}

	if len(res) == 0 {
		return "No dynamic environment variable added", nil
	}

	var sb strings.Builder
	sb.WriteString("Dynamic environment variables added:\n")

	vars, err := parseMultienvLine(res)
	if err != nil {
		return "", fmt.Errorf("Invalid environment variable definition: %s (%w)", res, err)
	}

	for i := 0; i < len(vars); i += 2 {
		key := vars[i]
		envs[key] = vars[i+1]
		sb.WriteString(key)
		sb.WriteRune('\n')
	}

	return sb.String(), nil
}