[Snyk] Security upgrade golang from 1.19.10 to 1.21rc3

[mefellows]

This PR was automatically created by Snyk using the credentials of a real user.

Keeping your Docker base image up-to-date means you’ll benefit from security fixes in the latest version of your chosen image. #### Changes included in this PR - Dockerfile We recommend upgrading to `golang:1.21rc3`, as this image has only 69 known vulnerabilities. To do this, merge this pull request, then verify your application still works as expected. Some of the most important vulnerabilities in your base image include: | Severity | Priority Score / 1000 | Issue | Exploit Maturity | | :------: | :-------------------- | :---- | :--------------- | |  | **436** | CVE-2023-32001
[SNYK-DEBIAN12-CURL-5783177](https://snyk.io/vuln/SNYK-DEBIAN12-CURL-5783177) | No Known Exploit | |  | **321** | Inappropriate Encoding for Output Context
[SNYK-DEBIAN12-OPENSSH-1556053](https://snyk.io/vuln/SNYK-DEBIAN12-OPENSSH-1556053) | Mature | |  | **221** | CVE-2023-2975
[SNYK-DEBIAN12-OPENSSL-5776700](https://snyk.io/vuln/SNYK-DEBIAN12-OPENSSL-5776700) | No Known Exploit | |  | **221** | CVE-2023-2975
[SNYK-DEBIAN12-OPENSSL-5776700](https://snyk.io/vuln/SNYK-DEBIAN12-OPENSSL-5776700) | No Known Exploit | |  | **221** | CVE-2023-3446
[SNYK-DEBIAN12-OPENSSL-5788322](https://snyk.io/vuln/SNYK-DEBIAN12-OPENSSL-5788322) | No Known Exploit | --- **Note:** _You are seeing this because you or someone else with access to this repository has authorized Snyk to open fix PRs._ For more information: 🧐 [View latest project report](https://app.snyk.io/org/pact-foundation-808/project/0c88a376-aac5-48c1-baa5-58b7ef92b022?utm_source=github&utm_medium=referral&page=fix-pr) 🛠 [Adjust project settings](https://app.snyk.io/org/pact-foundation-808/project/0c88a376-aac5-48c1-baa5-58b7ef92b022?utm_source=github&utm_medium=referral&page=fix-pr/settings) [//]: # 'snyk:metadata:{"prId":"7355c309-7cd7-4805-88f4-5a5e2b1ae5d0","prPublicId":"7355c309-7cd7-4805-88f4-5a5e2b1ae5d0","dependencies":[{"name":"golang","from":"1.19.10","to":"1.21rc3"}],"packageManager":"dockerfile","projectPublicId":"0c88a376-aac5-48c1-baa5-58b7ef92b022","projectUrl":"https://app.snyk.io/org/pact-foundation-808/project/0c88a376-aac5-48c1-baa5-58b7ef92b022?utm_source=github&utm_medium=referral&page=fix-pr","type":"auto","patch":[],"vulns":["SNYK-DEBIAN12-CURL-5783177","SNYK-DEBIAN12-OPENSSH-1556053","SNYK-DEBIAN12-OPENSSL-5776700","SNYK-DEBIAN12-OPENSSL-5788322"],"upgrade":["SNYK-DEBIAN12-CURL-5783177","SNYK-DEBIAN12-OPENSSH-1556053","SNYK-DEBIAN12-OPENSSL-5776700","SNYK-DEBIAN12-OPENSSL-5776700","SNYK-DEBIAN12-OPENSSL-5788322"],"isBreakingChange":false,"env":"prod","prType":"fix","templateVariants":["updated-fix-title","priorityScore"],"priorityScoreList":[436,321,221,221],"remediationStrategy":"vuln"}' --- **Learn how to fix vulnerabilities with free interactive lessons:** 🦉 [Learn about vulnerability in an interactive lesson of Snyk Learn.](https://learn.snyk.io/?loc=fix-pr)

[coveralls]

coverage: 37.338%. remained the same when pulling 50069465eeecc1e4e991907e45f32aa5abf9b924 on snyk-fix-d64b43a93a789f54c32b7f94673111be into 7d9ed69a2dc97e8e1a78a28eae8d76ce2e667b04 on master.