[BUG] github tests: build-linux ptl fails to heap_uncached_part failure

[kv2019i]

Describe the bug
Regression in commit 9cc7ad9

https://github.com/thesofproject/sof/actions/runs/20127912805/job/57761888407?pr=10429

 /__w/sof/sof/sof/src/audio/module_adapter/library/userspace_proxy.c: In function 'userspace_proxy_memory_init':
/__w/sof/sof/sof/src/audio/module_adapter/library/userspace_proxy.c:77:18: error: 'heap_part_cached' undeclared (first use in this function)
   77 |                 &heap_part_cached,
      |                  ^~~~~~~~~~~~~~~~

Problem uncovered when USERSPACE_PROXY was enabled in a default build target.

[kv2019i]

Can you take a look? This is visible in every PR now.