Add 'integration' tag to golangci-lint

[mrizzi]

Description of the PR

Added integration custom tag to .golangci.yaml configuration to solve CI Lint failure on main branch (ref. https://github.com/guacsec/guac/actions/runs/6021675765/job/16334972954):

golangci-lint run
pkg/assembler/backends/ent/backend/query_helpers.go:37:6: func `pkgTreeFromVersion` is unused (unused)
func pkgTreeFromVersion(ctx context.Context, pv *ent.PackageVersion) (*ent.PackageType, error) {
     ^
pkg/assembler/backends/ent/backend/query_helpers.go:72:6: func `buildPackageTreeQuery` is unused (unused)
func buildPackageTreeQuery(q *ent.PackageTypeQuery, ns, packageName string, pv *ent.PackageVersion) {
     ^

since methods are used from

guac/pkg/assembler/backends/ent/backend/package_test.go

Line 124 in 1e83043

pkgTree, err := pkgTreeFromVersion(s.Ctx, pkgVersion)

which has the //go:build integration tag

PR Checklist

• All commits have a Developer Certificate of Origin (DCO) -- they are generated using -s flag to git commit.
• All new changes are covered by tests
• If GraphQL schema is changed, make generate has been run
• If collectsub protobuf has been changed, make proto has been run
• All CI checks are passing (tests and formatting)
• All dependent PRs have already been merged

[mrizzi]

tilt ci job is expected to fail.
Fixed in #1201