Bump go from 1.20 to 1.21 in .github/workflows/quickstart_2.0.yml

[osamaesmailmsft]

Merge Checklist

All boxes should be checked before merging the PR (just tick any boxes which don't apply to this PR)

• The toolchain has been rebuilt successfully (or no changes were made to it)
• The toolchain/worker package manifests are up-to-date
• Any updated packages successfully build (or no packages were changed)
• Packages depending on static components modified in this PR (Golang, *-static subpackages, etc.) have had their Release tag incremented.
• Package tests (%check section) have been verified with RUN_CHECK=y for existing SPEC files, or added to new SPEC files
• All package sources are available
• cgmanifest files are up-to-date and sorted (./cgmanifest.json, ./toolkit/scripts/toolchain/cgmanifest.json, .github/workflows/cgmanifest.json)
• LICENSE-MAP files are up-to-date (./LICENSES-AND-NOTICES/SPECS/data/licenses.json, ./LICENSES-AND-NOTICES/SPECS/LICENSES-MAP.md, ./LICENSES-AND-NOTICES/SPECS/LICENSE-EXCEPTIONS.PHOTON)
• All source files have up-to-date hashes in the *.signatures.json files
• sudo make go-tidy-all and sudo make go-test-coverage pass
• Documentation has been updated to match any changes to the build system
• Ready to merge

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Summary

What does the PR accomplish, why was it needed?
The workflow Verify Quickstart 2.0 has been failing for an extended period of time, and this change fixes the simple issues.

Change Log

• Updated the prerequisites in .github/workflows/quickstart_2.0.yml to match those in 2.0's Quickstart README

Does this affect the toolchain?

NO

Test Methodology

• Running the workflow on this branch https://github.com/microsoft/azurelinux/actions/runs/12796263713

[jslobodzian]

@osamaesmailmsft please revert this change.