Rename example tests to pass go vet naming convention

[StevenACoffman]

Previously go vet would complain with:

# github.com/r3labs/diff/v3
./diff.go:100:2: struct field parent has json tag but is not exported
# github.com/r3labs/diff/v3_test
# [github.com/r3labs/diff/v3_test]
./diff_examples_test.go:13:1: ExamplePatchWithErrors refers to unknown identifier: PatchWithErrors
./diff_examples_test.go:173:1: ExamplePrimitiveSlice refers to unknown identifier: PrimitiveSlice
./diff_examples_test.go:257:1: ExampleComplexSlicePatch refers to unknown identifier: ComplexSlicePatch
./diff_examples_test.go:319:1: ExampleComplexMapPatch refers to unknown identifier: ComplexMapPatch
./diff_examples_test.go:596:1: ExamplePrivatePtr refers to unknown identifier: PrivatePtr

I did not correct line 100 in diff.go, since that might break backward compatibility, but this will help with the go test failure:
https://github.com/r3labs/diff/actions/runs/16860105094/job/47759060545