Fix retina check by making grep case insensitive

[BluBambu]

The imagesearcharea function wasn't working properly when used between a retina vs. non-retina external display on MacOS. After some basic debugging, it was due to the thumbnail not being scaled properly on the retina display.

The issue is due to the is_retina variable being determined via a case sensitive grep on system_profiler SPDisplaysDataType. The retina keyword is capitalized causing the grep to give a false negative:

system_profiler SPDisplaysDataType
Graphics/Displays:

    Apple M1 Max:

      Chipset Model: Apple M1 Max
      Type: GPU
      Bus: Built-In
      Total Number of Cores: 32
      Vendor: Apple (0x106b)
      Metal Family: Supported, Metal GPUFamily Apple 7
      Displays:
        Studio Display:
          Display Type: Retina LCD
          Resolution: 5120 x 2880 Retina
          Display Serial Number: ...
          Display Firmware Version: ...
          Main Display: Yes
          Mirror: Off
          Online: Yes
          Automatically Adjust Brightness: Yes

The fix is to make the grep case insensitive.

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Fix verified in python REPL:

Previous wrong output:

>>> subprocess.call("system_profiler SPDisplaysDataType | grep 'retina'", shell=True) == 0
False

Correct output with fix:

>>> subprocess.call("system_profiler SPDisplaysDataType | grep -i 'retina'", shell=True) == 0
          Display Type: Retina LCD
          Resolution: 5120 x 2880 Retina
True