Typo fix README.md (#1705)

# Pull Request: Typo Fix in `README.md`

## Description

This pull request fixes a typo in the `README.md` file of the
`subxt-tests` directory. The word **"directroy"** has been corrected to
**"directory"** for improved accuracy and readability.

## Changes Made

- Corrected the sentence in the `README.md` file:
> _This directroy contains integration tests against a real node using
`subxt`._
  - Updated to:
> _This directory contains integration tests against a real node using
`subxt`._

Signed-off-by: MaxweLL22-22 <vinyls-behest.2f@icloud.com>

Author: MaxweLL22-22