package grub-efi-amd64-signed 1.93.1+2.02-2ubuntu8.1 failed to install/upgrade: installed grub-efi-amd64-signed package post-installation script subprocess returned error exit status 1

I just tried to do an upgrade and got the following error during the installation of on e of the packages:
Installing for x86_64-efi platform.
Could not prepare Boot variable: No space left on device
grub-install: error: efibootmgr failed to register the boot entry: Input/output error.
Failed: grub-install --target=x86_64-efi --no-extra-removable
WARNING: Bootloader is not properly installed, system may not be bootable

I obviously cannot reboot/shutdown my pc since the chances of it not starting again are high.

More details can be found below:
Description: Ubuntu 18.04 LTS
Release: 18.04

grub-efi-amd64:
  Installed: 2.02-2ubuntu8.1
  Candidate: 2.02-2ubuntu8.1
  Version table:

ProblemType: Package
DistroRelease: Ubuntu 18.04
Package: grub-efi-amd64-signed 1.93.1+2.02-2ubuntu8.1
ProcVersionSignature: Ubuntu 4.15.0-24.26-generic 4.15.18
Uname: Linux 4.15.0-24-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
Date: Tue Jul 10 08:57:38 2018
ErrorMessage: installed grub-efi-amd64-signed package post-installation script subprocess returned error exit status 1
InstallationDate: Installed on 2018-01-17 (173 days ago)
InstallationMedia: Ubuntu 16.04.3 LTS "Xenial Xerus" - Release amd64 (20170801)
Python3Details: /usr/bin/python3.6, Python 3.6.5, python3-minimal, 3.6.5-3
PythonDetails: /usr/bin/python2.7, Python 2.7.15rc1, python-minimal, 2.7.15~rc1-1
RelatedPackageVersions:
 dpkg 1.19.0.5ubuntu2
 apt 1.6.2
SourcePackage: grub2-signed
Title: package grub-efi-amd64-signed 1.93.1+2.02-2ubuntu8.1 failed to install/upgrade: installed grub-efi-amd64-signed package post-installation script subprocess returned error exit status 1
UpgradeStatus: Upgraded to bionic on 2018-04-28 (72 days ago)