🐛 Update go version to 1.15 and tidy up modules

[Adirio]

Background

regexp.Regexp.SubexpIndex was added in 1.15 and despite using that method, go.mod still is in 1.14:

kubebuilder-release-tools/notes/go.mod

Line 3 in 7259830

go 1.14

kubebuilder-release-tools/notes/compose/notes.go

Lines 45 to 46 in 7259830

	minorRaw := parts[releaseRE.SubexpIndex("minor")]
	majorRaw := parts[releaseRE.SubexpIndex("major")]

go-git is not being used but it still figures in go.mod:

kubebuilder-release-tools/notes/go.mod

Line 7 in 7259830

github.com/go-git/go-git/v5 v5.1.0

Description

This PR updates the go version in go.mod and tidies the modules to remove go-git.

[camilamacedo86]

It shows great for me 🥇 .

However, I since I have not further knowledge in the kubebuilder-release-tools (I never push a PR and etc for this one), I think is good +1 person checkout as well.

[fejta-bot]

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Mark the issue as fresh with /remove-lifecycle stale.
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Send feedback to sig-contributor-experience at kubernetes/community.
/lifecycle stale

[vincepri]

/lgtm
/assign @DirectXMan12

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Adirio, camilamacedo86, vincepri

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