Simplified test

[radarhere]

Suggestions for python-pillow#8350

• If we're going to artificially create a test image, instead of doing it beforehand and adding another 54kb to the test suite, let's just create the EXIF header in code.
• I understand you're mimicking the test code from Handle EXIF data truncated to just the header python-pillow/Pillow#6124, but that was for when the Exif data immediately stopped after the header. Your scenario is for two headers and then the rest of the data, almost the opposite of that. So I don't think we need to add a dedicated test for when there are two Exif headers and then the data stops. And rather than testing for just emptiness or not of the EXIF data, let's check one of the values inside.

[zakajd]

I like this way, let's do that. Will update PR soon