Bump Helix workitem timeout for libraries outerloop runs (#49876)

System.IO.Compression.Brotli.Tests takes 870 seconds already which is quite close to the 900s timeout.

src/libraries/sendtohelixhelp.proj

@@ -29,6 +29,7 @@
     <_workItemTimeout Condition="'$(Scenario)' == '' and '$(_workItemTimeout)' == '' and ('$(TargetArchitecture)' == 'arm64' or '$(TargetArchitecture)' == 'arm')">00:45:00</_workItemTimeout>
     <_workItemTimeout Condition="'$(Scenario)' != '' and '$(_workItemTimeout)' == '' and ('$(TargetArchitecture)' == 'arm64' or '$(TargetArchitecture)' == 'arm')">01:00:00</_workItemTimeout>
     <_workItemTimeout Condition="'$(Scenario)' == 'BuildWasmApps' and '$(_workItemTimeout)' == ''">01:00:00</_workItemTimeout>
+    <_workItemTimeout Condition="'$(Scenario)' == '' and '$(_workItemTimeout)' == '' and '$(Outerloop)' == 'true'">00:20:00</_workItemTimeout>
     <_workItemTimeout Condition="'$(Scenario)' == '' and '$(_workItemTimeout)' == ''">00:15:00</_workItemTimeout>
     <_workItemTimeout Condition="'$(Scenario)' != '' and '$(_workItemTimeout)' == ''">00:30:00</_workItemTimeout>