Bump golang version to 1.21 in devfile-gem

MR: https://gitlab.com/gitlab-org/remote-development/devfile-gem/-/merge_requests/44

Description

Bump golang version to 1.21.0 in the devfile gem to address the following issues

• https://gitlab.com/gitlab-org/build/CNG/-/issues/549

Acceptance Criteria

• Devfile gem has golang version updated to 1.21.0
• Devfile gem with this version is published to rubygems.org
• Rails is updated with the latest version of the devfile gem
• Locally verify that this update works does not introduce any regression issues

Technical Requirements

Since this upgrade requires no update to the business logic, the technical requirements are the same as the acceptance criteria

Design Requirements

NA

Impact Assessment

No regression issues should be introduced as a part of this upgrade

User Story

NA