Fix Docker patch step for ROCm >= 7.0: escape 'purelib' key in sysconfig call

The Docker build fails during the namespace patch step for ROCm >= 7.0 with:

NameError: name 'purelib' is not defined

This is caused by unescaped single quotes around ['purelib'] inside a double-quoted
Python command within bash -c, which Bash misinterprets as a shell variable.

We fix this by switching to a single-quoted Python command and using double quotes
for the dictionary key access:

python3 -c 'import sysconfig; print(sysconfig.get_paths()["purelib"])'

Note: This issue does not occur in CI with ROCm 6.4.1 because the patch step is
only triggered for ROCm versions 7.0 and above.