VAULT-41529: fix filtering by variant and no scenario name

[ryancragun]

How to read this pull request

When we rewrote scenario filtering to be a decode time operation we missed a case that resulted in broken filtering. If we given a filter that includes variants but does not include a scenario name the list would return scenarios with matching variants but would also include the scenario name of scenarios that either didn't have a matrix defined or had no matrix variants that matched. This fixes it to exclude scenario blocks that have no matching variants when given such filters.

Before

> enos scenario list arch:arm64 artifact_source:crt artifact_type:bundle backend:raft config_mode:file consul_edition:ce consul_version:1.18.2 distro:sles edition:ent ip_version:6 seal:awskms
NAME                VARIANTS

agent               arch:arm64  artifact_source:crt  artifact_type:bundle  backend:raft  config_mode:file  consul_edition:ce  consul_version:1.18.2  distro:sles  edition:ent  ip_version:6  seal:awskms
autopilot           arch:arm64  artifact_source:crt  artifact_type:bundle  backend:raft  config_mode:file  consul_edition:ce  consul_version:1.18.2  distro:sles  edition:ent  ip_version:6  seal:awskms
benchmark
cloud
dev_pr_replication
dev_single_cluster
dr_replication
pr_replication
proxy               arch:arm64  artifact_source:crt  artifact_type:bundle  backend:raft  config_mode:file  consul_edition:ce  consul_version:1.18.2  distro:sles  edition:ent  ip_version:6  seal:awskms
seal_ha
smoke               arch:arm64  artifact_source:crt  artifact_type:bundle  backend:raft  config_mode:file  consul_edition:ce  consul_version:1.18.2  distro:sles  edition:ent  ip_version:6  seal:awskms
ui                  arch:arm64  artifact_source:crt  artifact_type:bundle  backend:raft  config_mode:file  consul_edition:ce  consul_version:1.18.2  distro:sles  edition:ent  ip_version:6  seal:awskms
upgrade             arch:arm64  artifact_source:crt  artifact_type:bundle  backend:raft  config_mode:file  consul_edition:ce  consul_version:1.18.2  distro:sles  edition:ent  ip_version:6  seal:awskms

After

> enos scenario list arch:arm64 artifact_source:crt artifact_type:bundle backend:raft config_mode:file consul_edition:ce consul_version:1.18.2 distro:sles edition:ent ip_version:6 seal:awskms
NAME       VARIANTS

agent      arch:arm64  artifact_source:crt  artifact_type:bundle  backend:raft  config_mode:file  consul_edition:ce  consul_version:1.18.2  distro:sles  edition:ent  ip_version:6  seal:awskms
autopilot  arch:arm64  artifact_source:crt  artifact_type:bundle  backend:raft  config_mode:file  consul_edition:ce  consul_version:1.18.2  distro:sles  edition:ent  ip_version:6  seal:awskms
proxy      arch:arm64  artifact_source:crt  artifact_type:bundle  backend:raft  config_mode:file  consul_edition:ce  consul_version:1.18.2  distro:sles  edition:ent  ip_version:6  seal:awskms
smoke      arch:arm64  artifact_source:crt  artifact_type:bundle  backend:raft  config_mode:file  consul_edition:ce  consul_version:1.18.2  distro:sles  edition:ent  ip_version:6  seal:awskms
ui         arch:arm64  artifact_source:crt  artifact_type:bundle  backend:raft  config_mode:file  consul_edition:ce  consul_version:1.18.2  distro:sles  edition:ent  ip_version:6  seal:awskms
upgrade    arch:arm64  artifact_source:crt  artifact_type:bundle  backend:raft  config_mode:file  consul_edition:ce  consul_version:1.18.2  distro:sles  edition:ent  ip_version:6  seal:awskms

Checklist

• The commit message includes an explanation of the changes
• Manual validation of the changes have been performed (if possible)
• New or modified code has requisite test coverage (if possible)
• I have performed a self-review of the changes
• I have made necessary changes and/or pull requests for documentation
• I have written useful comments in the code