Fix: egrep is obsolescent, use grep -E

See e.g., egrep(1) [https://linux.die.net/man/1/egrep]:

> two variant programs egrep and fgrep are available. egrep is the same
> as grep -E. fgrep is the same as grep -F. Direct invocation as either
> egrep or fgrep is deprecated

See also the rationale of the POSIX description of grep
(https://pubs.opengroup.org/onlinepubs/9699919799/utilities/grep.html):

> This grep has been enhanced in an upwards-compatible way to provide
> the exact functionality of the historical egrep and fgrep commands as
> well. It was the clear intention of the standard developers to
> consolidate the three greps into a single command.

Closes: #839

ci-scripts/doGitLabMerge.sh

@@ -126,7 +126,7 @@ git config user.email "jenkins@openairinterface.org"
 git config user.name "OAI Jenkins"
 
 git checkout -f $SOURCE_COMMIT_ID > checkout.txt 2>&1
-STATUS=`egrep -c "fatal: reference is not a tree" checkout.txt`
+STATUS=`grep -E -c "fatal: reference is not a tree" checkout.txt`
 rm -f checkout.txt
 if [ $STATUS -ne 0 ]
 then
@@ -137,7 +137,7 @@ fi
 
 git merge --ff $TARGET_COMMIT_ID -m "Temporary merge for CI"
 
-STATUS=`git status | egrep -c "You have unmerged paths.|fix conflicts"`
+STATUS=`git status | grep -E -c "You have unmerged paths.|fix conflicts"`
 if [ $STATUS -ne 0 ]
 then
     echo "There are merge conflicts.. Cannot perform further build tasks"