psensor: add -Wno-error due to increasing compiler strictness
psensor: add -Wno-error due to increasing compiler strictness

This Hydra failure:

  https://hydra.nixos.org/log/iq8zqmw7yclgwpvr8i8clwf2sh67jb0i-psensor-1.2.1.drv

...appears to be the result of the package shipping with -Werror and
gcc accreting ever-increasing quantities of warnings as time
progresses.  Let's not treat the compiler warnings as errors.

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