sigrokdriver: fix TypeError in stop() by passing bytes to communicate()

[xistadi]

Popen is opened without text=True so stdin is in binary mode. communicate(input=...) must receive bytes, not str. Fixes Python 3.11+ TypeError: memoryview requires bytes, not str.

Fixes #1847

SigrokDriver.stop() calls self._process.communicate(input="q"), but
Popen is created without text=True, so stdin is in binary mode.
On Python 3.11+, this raises:
TypeError: memoryview: a bytes-like object is required, not 'str'
Fix: pass b"q" instead of "q".

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 45.8%. Comparing base (3912486) to head (bda43fd).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
labgrid/driver/sigrokdriver.py	0.0%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #1850   +/-   ##
======================================
  Coverage    45.8%   45.8%           
======================================
  Files         182     182           
  Lines       14718   14718           
======================================
  Hits         6743    6743           
  Misses       7975    7975           

Flag	Coverage Δ
3.10	45.8% <0.0%> (ø)
3.11	45.8% <0.0%> (ø)
3.12	45.8% <0.0%> (ø)
3.13	45.7% <0.0%> (ø)
3.14	45.7% <0.0%> (ø)

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[Emantor]

Hi, you will need to fix the DCO error by adding your Signed-off-by, see DCO site.

[xistadi]

Hi, you will need to fix the DCO error by adding your Signed-off-by, see DCO site.

Hey! Fixed