Insomnia plugin always adding a ';' at the end of the string when used in the Headers section

### Expected Behavior

Insomnia plugin should return the string as is

### Actual Behavior

When i look at the timeline of the request, I see there is a ';' character added at the end.

### Reproduction Steps

Install https://github.com/mageshwaranr/insomnia-plugin-sh-cmd plugin
use "execute a command" option in the bulk edit headers
make a request

### Is there an existing issue for this?

- [X] I have searched the [issue tracker](https://www.github.com/Kong/insomnia/issues) for this problem.

### Additional Information

The plugin is quite simple actually

```
const { promisify } = require('util');
const exec = promisify(require('child_process').exec)

module.exports.templateTags = [
{
displayName: "/bin/sh",
name: "shCmdExec",
description:
"Executes given command using child_process package, basically /bin/sh cmd",
args: [
{
displayName: "Type",
type: "enum",
options: [
{
displayName: "Execute command returning String value",
value: "string",
},
{
displayName: "Execute command returning JSON value",
value: "json",
},
],
},
{
displayName: "Command/shell to be executed",
help: 'Executes the given command using require("child_process").exec command',
type: "string",
},
],
async run(context, type = "string", cmd) {
try {
var resp = await exec(cmd)
} catch (failed) {
console.log("Command execution failed with " + failed)
return failed.stderr
}

if (type == "json") {
return JSON.parse(resp.stdout.trim()) // add test case
}
return resp.stdout.trim()
},
},
]
```
If I copy/paste the values from the live preview field, it works, but not as a variable.

### Insomnia Version

2021.7.2

### What operating system are you using?

macOS

### Operating System Version

Macos Big Sur 11.6.3

### Installation method

homebrew

### Last Known Working Insomnia version

_No response_

Reproduce the issue with the insomnia-plugin-sh-cmd template tag in bulk-edit Headers, then compare the live preview with the request shown in the timeline. Trace the template-tag value through request construction and verify that the header value remains unchanged when the request is sent.

Written by the indexing model from the issue text.