tests/gem_exec_capture: adjust the pi subtest

This was broken by the kernel change: 71b1669ea9bd ("drm/i915/uapi:
tweak error capture on recoverable contexts"). Update the test to use
non-recoverable context if needed.

Closes: intel#6350
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Nirmoy Das <nirmoy.das@linux.intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
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