enable web_long_running_tests shard (#69350)

dev/prod_builders.json

@@ -132,6 +132,12 @@
          "task_name": "linux_web_integration_tests",
          "flaky": false
       },
+      {
+         "name": "Linux web_long_running_tests",
+         "repo": "flutter",
+         "task_name": "linux_web_long_running_tests",
+         "flaky": false
+      },
       {
          "name":"Linux web_e2e_test",
          "repo":"flutter",

dev/try_builders.json

@@ -153,6 +153,13 @@
          "enabled":true,
          "run_if":["dev/", "packages/flutter/", "packages/flutter_test/", "packages/flutter_tools/", "packages/flutter_web_plugins/", "bin/"]
       },
+      {
+         "name": "Linux web_long_running_tests",
+         "repo":"flutter",
+         "task_name":"web_long_running_tests",
+         "enabled":true,
+         "run_if":["dev/", "packages/", "bin/"]
+      },
       {
         "name":"Linux web_e2e_test",
         "repo":"flutter",