Installation script shouldn't rely on server other than AGH being present

### Prerequisites

- [X] I have checked the [Wiki](https://github.com/AdguardTeam/AdGuardHome/wiki) and [Discussions](https://github.com/AdguardTeam/AdGuardHome/discussions) and found no answer

- [X] I have searched other issues and found no duplicates

- [X] I want to report a bug and not ask a question

### Operating system type

Other (please mention in the description)

### CPU architecture

Other (please mention in the description)

### Installation

GitHub releases or script from README

### Setup

Other (please mention in the description)

### AdGuard Home version

v0.107.8

### Description

#### What did you do?

Try the install script to reinstall/update AGH on a machine where AGH is the only configured DNS server.

#### Expected result

Successful reinstallation/update.

#### Actual result

Since AGH is the only DNS server, once the previous installation is stopped, there is no way for `curl`/`wget` to resolve the address of the static storage from which AGH is downloaded. So, the process fails.

#### Additional information

This is unrelated to architectures, and is relevant to unix OSes, on which the script works.

@Alex-302, please confirm that the description is correct.