ci: require gcovr 5.1 for code coverage reports

Stop passing `-j`, it wasn't very useful and it's broken in gcovr 5.1

Change-Id: I7194eda57262d63199006baa36c81144ef8053f0
diff --git a/.jenkins.d/00-deps.sh b/.jenkins.d/00-deps.sh
index 0b589d5..cd4afee 100755
--- a/.jenkins.d/00-deps.sh
+++ b/.jenkins.d/00-deps.sh
@@ -31,7 +31,7 @@
     case $JOB_NAME in
         *code-coverage)
             sudo apt-get -qy install lcov python3-pip
-            pip3 install --user --upgrade --upgrade-strategy=eager 'gcovr~=5.0'
+            pip3 install --user --upgrade --upgrade-strategy=eager 'gcovr~=5.1'
             ;;
         *Docs)
             sudo apt-get -qy install doxygen graphviz