Fixup enums.xml user policy name for TabUnderAllowed

The TabUnderProtectionEnabled policy was renamed to TabUnderAllowed in
CL:995632.
Rename the value in enums.xml too.

Bug: b/77374536
Change-Id: I0eede70c436b4e5260cb02e19838f2d22528594c
Reviewed-on: https://chromium-review.googlesource.com/1035322Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Pavol Marko <pmarko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557155}

tools/metrics/histograms/enums.xml

@@ -13156,7 +13156,7 @@ Called by update_net_error_codes.py.-->
   <int value="429" label="SafeBrowsingExtendedReportingEnabled"/>
   <int value="430" label="AutoplayAllowed"/>
   <int value="431" label="AutoplayWhitelist"/>
-  <int value="432" label="TabUnderProtectionEnabled"/>
+  <int value="432" label="TabUnderAllowed"/>
   <int value="433" label="UserNativePrintersAllowed"/>
   <int value="434" label="DefaultWebUsbGuardSetting"/>
   <int value="435" label="CertificateTransparencyEnforcementDisabledForCas"/>