bazel: mark envtests as "requires-network"

Envtests require networking, strict sandbox only allows networking if tag is set.
See https://bazel.build/reference/be/common-definitions#common.tags for further explanation.

operators/constellation-node-operator/controllers/BUILD.bazel

@@ -75,6 +75,8 @@ go_test(
     },
     # keep
     gotags = ["integration"],
+    # keep
+    tags = ["requires-network"],
     deps = [
         "//3rdparty/node-maintenance-operator/api/v1beta1",
         "//internal/constants",