New issue by ackalker on void-packages repository

https://github.com/void-linux/void-packages/issues/12499
Description: ### System

* xuname:  
  Void 5.1.10_1 x86_64 GenuineIntel uptodate rrrrmdFFFFFFFFF
* package:  
  efibootmgr-17_2

### Expected behavior

Installing a new kernel or force reconfiguring an already installed kernel should create or update a boot entry that actually boots that kernel.

### Actual behavior

The generated boot entry for booting EFISTUB kernel gets rejected by my UEFI firmware because the binary file name (for example `vmlinuz-5.1.10_1` lacks an `.efi` extension.
In contrast to what some documentation on the Internet says, the `.efi` extension is *not* optional; it is *required* by the UEFI specs for all EFI applications, no exceptions. Just because some UEFI versions on some mainboards will run EFI applications from files without an `.efi` extension doesn't mean this is true for all UEFI versions in general.

### Steps to reproduce the behavior

- Boot the system in UEFI mode
- Install `efibootmgr` package
- Make sure that `/etc/default/efibootmgr-kernel-hook` contains uncommented line `MODIFY_EFI_ENTRIES=1` and appropriate `OPTIONS="..."` value for that kernel
- Install or force reconfigure a kernel
- (optional) Reconfigure boot order using `efibootmgr -o ...`