Rollup merge of #49886 - varkor:generate-deriving-span-tests-usability, r=nikomatsakis
Rollup merge of #49886 - varkor:generate-deriving-span-tests-usability, r=nikomatsakis

Ignore copyright year when generating deriving span tests

Previously, generate-deriving-span-tests.py would regenerate all the tests anew, even if they hadn't changed. This creates unnecessary diffs that only change the copyright year. Now we check to see if any of the content of the test has changed before generating the new one.

GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,GBGamer/rust