Fix empty and len testifylint violations across test files

[mmorel-35]

Removes empty and len from testifylint's disable list and fixes all 21 violations across 13 test files.

Rule changes:

• len: assert.Equal(t, n, len(x)) / is.Equal(n, len(x)) → assert.Len(t, x, n) / is.Len(x, n)
• empty: assert.Len(t, x, 0), assert.Equal(t, "", x), is.Equal(0, len(x)), is.NotEqual(len(x), 0) → assert.Empty / assert.NotEmpty / is.Empty / is.NotEmpty

Files updated: internal/chart/v3/chart_test.go, pkg/chart/v2/chart_test.go, internal/chart/v3/lint/rules/crds_test.go, pkg/chart/v2/lint/rules/crds_test.go, internal/plugin/loader_test.go, pkg/action/action_test.go, pkg/action/get_metadata_test.go, pkg/action/install_test.go, pkg/action/list_test.go, pkg/action/upgrade_test.go, pkg/engine/files_test.go, pkg/kube/client_test.go, pkg/registry/registry_test.go, .golangci.yml

Special notes for your reviewer:

All changes are mechanical assertion rewrites; semantics are identical.

If applicable:

• this PR contains user facing changes (the docs needed label should be applied if so)
• this PR contains unit tests
• this PR has been tested for backwards compatibility

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR aligns Go tests with testifylint recommendations by replacing manual len(...)/empty-string checks with more idiomatic Testify assertions, and updates lint configuration to enforce these rules.

Changes:

• Replace Equal(..., len(x)) and Len(..., 0) patterns with Len, Empty, and NotEmpty assertions across multiple test packages.
• Enable testifylint’s empty and len checks in .golangci.yml by removing them from the disabled list.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
pkg/registry/registry_test.go	Uses suite.Len instead of Equal(1, len(tags)) for tag count assertions.
pkg/kube/client_test.go	Uses assert.Empty for zero-length created/deleted result sets in rollback test.
pkg/engine/files_test.go	Uses assert.Empty for empty string assertion.
pkg/chart/v2/lint/rules/crds_test.go	Uses assert.Empty for no lint messages.
pkg/chart/v2/chart_test.go	Uses assert.Len for CRD count.
pkg/action/upgrade_test.go	Uses assert.Empty for dependency list emptiness.
pkg/action/list_test.go	Uses assert.Empty for empty result lists.
pkg/action/install_test.go	Uses assert.NotEmpty for manifest non-emptiness, assert.Empty for empty output buffer.
pkg/action/get_metadata_test.go	Uses assert.Empty for empty alias/app version strings.
pkg/action/action_test.go	Uses assert.Len for reconstructed/maps size checks; uses assert.Empty for empty notes.
internal/plugin/loader_test.go	Uses assert.Empty for empty plugin list.
internal/chart/v3/lint/rules/crds_test.go	Uses assert.Empty for no lint messages.
internal/chart/v3/chart_test.go	Uses assert.Len for CRD count.
.golangci.yml	Enables testifylint empty and len rules by removing them from the disable list.

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[TerryHowe]

/lgtm