ci: validate input tag before provisioning and running packaging tests

[sairaj18]

• Update the prerelease-testing workflow to validate the input tag.
• The input tag should be the latest pre-release tag because the workflow will run provision test in amd64, arm64 linux instances which will try to install the latest available infra-agent version from staging repo.
• Add validate-tag job as dependency to test-prerelease-linux job.

Testing details:

• Input valid tag the validate-tag job succeeded - https://github.com/newrelic/infrastructure-agent/actions/runs/16462116536
• Input invalid tag the validate-tag job failed - https://github.com/newrelic/infrastructure-agent/actions/runs/16462125404

[coveralls]

Pull Request Test Coverage Report for Build 16466020648

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.03%) to 57.399%

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Files with Coverage Reduction	New Missed Lines	%
pkg/metrics/sampler/sampler_routine.go	2	95.35%

Totals
Change from base Build 16417112651:	0.03%
Covered Lines:	15407
Relevant Lines:	26842

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💛 - Coveralls