Update tfb-startup.sh (#8066)

Startup script missing the USER_ID env var added in https://github.com/TechEmpower/FrameworkBenchmarks/pull/8021 causing service to fail on Citrine

toolset/continuous/tfb-startup.sh

@@ -25,6 +25,7 @@ docker build -t techempower/tfb .
 
 echo "running tfb docker image"
 docker run \
+  -e USER_ID=$(id -u) \
   --network=host \
   --mount type=bind,source=$TFB_REPOPARENT/$TFB_REPONAME,target=/FrameworkBenchmarks \
   techempower/tfb \