[maven plugin] fix security issues

[wing328]

• Use Files.createTempFile instead

cc @OpenAPITools/generator-core-team

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[JLLeitschuh]

Having a hard time spotting where the temporary directory comes from that could sink to this location. Can you point out the line?

[wing328]

The change simply checks to ensure the directory is created successfully. This is not to say without these lines, there's a security issue.

[JLLeitschuh]

Makes sense!

[spacether]

Looks good to me!