This is a regression from #12864. The underscore is now too thin when the document is zoomed in.

URL: https://github.com/mozilla/pdf.js/files/2321540/issue6127.pdf
PDF.js 2.7.526: https://i.imgur.com/T4mIpct.png
PDF.js 2.7.510: https://i.imgur.com/nbwEpGT.png
Adobe Acrobat Reader DC 2020.013.20074: https://i.imgur.com/wDFBf3R.png

The screenshots were taken at 400% zoom.
if (!this.contentVisible) {
      return;
    }
    this.restore();
    this.baseTransform = this.baseTransformStack.pop();
  }
  beginGroup(group) {
    if (!this.contentVisible) {
      return;
    }
    this.save();
    
    
    const suspendedCtx = this.suspendedCtx;
    if (this.current.activeSMask) {
      this.suspendedCtx = null;
      this.current.activeSMask = null;
    }
    const currentCtx = this.ctx;