Misleading clock speed on Nano Every product listing on Arduino Store

### Describe the problem

https://store.arduino.cc/nano-every

The "Tech Specs" tab of the Nano Every store page says:

> |||
> |-|-|
> |Clock Speed|20MHz|

but the "**Arduino megaAVR Boards**" platform is intentionally configured to run this board at 16 MHz:

https://github.com/arduino/ArduinoCore-megaavr/blob/5e639ee40afa693354d3d056ba7fb795a8948c11/boards.txt#L67

Although the board is capable of running at 20 MHz, to do so would require the user to modify the **Arduino megaAVR Boards** platform, which is a fairly advanced process. For this reason, I feel the 20 MHz clock speed stated on the store page is a bit misleading and should be changed to:

> |||
> |-|-|
> |Clock Speed|16 MHz (20 MHz max)|

### Additional context

Originally reported at https://forum.arduino.cc/t/clock-speed-for-nano-every/599449

#### Related

- https://github.com/arduino/docs-content/pull/2357
- I believe this only corrects the information on [the Nano Every documentation page](https://docs.arduino.cc/hardware/nano-every/#tech-specs). If so, it does not fix this issue as this issue is about the misleading information on [the store page](https://store.arduino.cc/nano-every).

#### Additional reports

- https://forum.arduino.cc/t/nano-v3-nano-every-mcufriend_kbv-library-no-longer-working/598351/3
- https://forum.arduino.cc/t/arduino-nano-every-review/697136/4

Review the Nano Every Tech Specs tab at the Arduino Store URL and compare its clock-speed entry with boards.txt line 67 in ArduinoCore-megaavr. Check related docs-content pull request 2357 to distinguish the documentation-page change from the store listing; done means the store page clearly states 16 MHz (20 MHz max).

Written by the indexing model from the issue text.