[Bug]: "Invalid regular expression" in process.env causes build-storybook to crash

[hoovercj]

Describe the bug

It is possible to have values in process.env that cause the build-storybook command to crash because template.ts assumes that the value will be a valid regex.

This code in node_modules\@storybook\manager-webpack5\dist\cjs\presets\manager-preset.js has this code:

case 9:
  template = _context.sent;
  _context.next = 12;
  return presets.apply('managerHead', (0, _coreCommon.getManagerHeadTemplate)(configDir, process.env));

which directly passes process.env to getManagerHeadTemplate, which in turn passes those values directly to interpolate.

To Reproduce

We had some markdown content similar to [link](https://github.com/?_a) which was in an environment variable which somehow led to the error:

SyntaxError: InvalidRegularExpression: /%[here](https://github.com?_a%/: Unterminated group

I don't know how the trailing ) was lost but either way, even if we have something that appears to be an invalid regex in our environment variables, we don't expect build_storybook to fail.

System

Windows

Additional context

No response