On the fly request body gzipping is broken by utf-8 default encoding

### Expected behavior

Given API under test requires gzipped json body,
And I created HTTPSampler with a [JSR223 preprocessor, which compresses request](https://stackoverflow.com/a/33741293/7940542)
When I run tests
Then server returns 200 reponse code.

### Actual behavior

Then server returns 500 code, and says 'not in gzip format'

### Steps to reproduce the problem

[Test Plan.jmx.gz](https://github.com/apache/jmeter/files/13636162/Test.Plan.jmx.gz)

Was broken in 7450e4b0497c9a37c44852912e8d3dc2d0ee644e(fix: use UTF-8 as a default encoding in HTTP sampler)

### JMeter Version

5.6.1

### Java Version

openjdk 17.0.8 2023-07-18

### OS Version

Debian GNU/Linux 12 (bookworm)