fix(framework): validate all ReplicatedJobs in Volcano priorityClassName check

[Abhishek86798]

What this PR does / why we need it

Volcano.Validate iterates jobSetSpec.ReplicatedJobs to check each job's priorityClassName. When a ReplicatedJob used a reserved priority class (system-cluster-critical or system-node-critical), the loop returned early instead of continuing to the next job, so validation was silently skipped for every ReplicatedJob listed after it.

This meant a TrainJob could be admitted with an invalid priorityClassName on a later ReplicatedJob, only surfacing as a pod scheduling failure at runtime instead of being rejected at admission time.

This PR:

• changes the early return nil, allErrs to continue so each ReplicatedJob is validated independently;
• adds table-driven test cases covering a reserved-priority job followed by an invalid one (should still error), and multiple reserved-priority jobs together (should produce no errors) — the existing suite only covered single-ReplicatedJob scenarios.

Validation

• go build ./...
• go vet ./...
• go test ./pkg/runtime/framework/plugins/volcano/... -run TestValidate -v — all cases pass, including the two new ones.

Fixes #3917

[google-oss-prow]

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[Abhishek86798]

Friendly ping on this one — it's a small fix (early return inside a loop that should be continue, so priorityClassName validation is skipped for every ReplicatedJob after one using a reserved critical priority class), with table-driven test coverage for the multi-ReplicatedJob cases the existing suite didn't reach.

Happy to rebase or adjust if anything needs changing. cc @robert-bell @kuizhiqing