[Automation] Bump Golang version to 1.20.6

[apmmachine]

It requires the version to be bumped first in golang-crossbuild project, then a new release will be added to:
https://github.com/elastic/golang-crossbuild/releases/tag/v1.20.6.
Otherwise it will fail until the docker images are available.

---

Bump golang-version to latest version

Update from dockerfiles

Updated to content "ARG GO_VERSION=1.20.6" in file "Dockerfile" Updated to content "ARG GO_VERSION=1.20.6" in file "Dockerfile.skaffold"

1.20.6

no GitHub Release found for go1.20.6 on "https://github.com/golang/go"

Update go.mod

Updated to content "go 1.20" in file "go.mod"

Update .go-version

Updated to content "1.20.6" in file ".go-version"

1.20.6

no GitHub Release found for go1.20.6 on "https://github.com/golang/go"

Update .golangci.yml

Updated to content "1.20.6" in file ".golangci.yml"

1.20.6

no GitHub Release found for go1.20.6 on "https://github.com/golang/go"

Update version.asciidoc

Updated to content ":go-version: 1.20.6" in file "version/docs/version.asciidoc"

1.20.6

no GitHub Release found for go1.20.6 on "https://github.com/golang/go"

---

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[elasticmachine]

💚 Build Succeeded

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Build stats

• Start Time: 2023-07-25T15:58:36.312+0000

• Duration: 64 min 33 sec

Test stats 🧪

Test	Results
Failed	0
Passed	6099
Skipped	27
Total	6126

💚 Flaky test report

Tests succeeded.

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• /test : Re-trigger the build.

• /package : Generate the packages.

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[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	98.718% (77/78)	👍
Files	68.657% (184/268)	👍
Classes	67.606% (336/497)	👍
Methods	54.222% (1053/1942)	👍
Lines	40.328% (12044/29865)	👎 -0.02
Conditionals	100.0% (0/0)	💚

[cmacknz]

/test

[cmacknz]

/test

[cmacknz]

buildkite test it