Bump default enterprise gateway image

It seems that we've neglected the `DefaultEnterpriseImageTag` leaving it at `2.7`

https://github.com/Kong/kubernetes-testing-framework/blob/6cfb2cb793826053834fef949ff5f3f5a271874d/pkg/clusters/addons/kong/addon.go#L50-L51

The outcome of this, given that we use defaults in KIC:

https://github.com/Kong/kubernetes-ingress-controller/blob/3ce7c14afd2099e991c4dcd3370f23ef8c742a5e/test/internal/helpers/ktf.go#L18-L30

is that we've been skipping tests in KIC that we didn't intend to skip: https://github.com/Kong/kubernetes-ingress-controller/actions/runs/4086412787/jobs/7045676471#step:7:15296

```
=== Skipped
=== SKIP: test/integration TestIngressRegexMatchPath (0.00s)
ingress_regex_match_test.go:32: regex prefixes are only relevant for Kong 3.0+

=== SKIP: test/integration TestIngressRegexMatchHeader (0.00s)
ingress_regex_match_test.go:186: regex prefixes are only relevant for Kong 3.0+

=== SKIP: test/integration TestIngressClassRegexToggle (1.00s)
ingress_test.go:565: legacy regex detection is only relevant for Kong 3.0+

=== SKIP: test/integration TestIngressRegexPrefix (0.00s)
ingress_test.go:698: regex prefixes are only relevant for Kong 3.0+

=== SKIP: test/integration TestIngressRecoverFromInvalidPath (0.00s)
ingress_test.go:861: the case TestIngressRecoverFromInvalidPath should be run separately; please set TEST_RUN_INVALID_CONFIG_CASES to true to run this case

=== SKIP: test/integration TestPluginOrdering (1.00s)
plugin_test.go:207: plugin ordering requires Kong Enterprise 3.0+
```

Open pkg/clusters/addons/kong/addon.go at DefaultEnterpriseImageTag and determine the intended current enterprise gateway tag from the referenced KIC compatibility and skipped-test context. Update the default and verify that the affected KIC integration tests are no longer skipped for requiring Kong Enterprise 3.0+.

Written by the indexing model from the issue text.