Add fetch-depth: 0 to examples

[massongit]

level=warning msg="[runner] Can't process result by diff processor: can't prepare diff by revgrep: could not read git repo: error executing git diff \"b00bface\" \"\": exit status 128"

In order to prevent this golangci-lint's warning, it is necessary to give fetch-depth: 0 to actions/checkout: golangci/golangci-lint#161 (comment)
Therefore, I modify README accordingly.

[review-dog]

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