postinst: avoid false positives when scanning logs for errors

Replace deprecated egrep usage with grep -E and improve the log
matching pattern to avoid false positives.

Previously, the pattern 'warn|error|fatal|fail' matched substrings
such as 'str_error_r.o' and triggered failures due to the egrep
deprecation warning.

Updated the command to use:
grep -Eiw 'warn(ing)?|error|fatal|fail'

This ensures only whole words are matched and includes both 'warn'
and 'warning', reducing incorrect test failures.

Signed-off-by: AshwinUjjwal <ashwinujjwal.bharti@emerson.com>

Author: AshwinUjjwal

recipes-devtools/run-postinsts/files/test-run-postinsts-log.sh

@@ -20,7 +20,7 @@ source "$CONFIG_FILE" || fail "Failed to run $CONFIG_FILE"
 
 # only present on first boot
 if [ -e "$LOGFILE" ]; then
-    if egrep -i 'warn|error|fatal|fail' "$LOGFILE"; then
+    if grep -Eiw 'warn(ing)?|error|fatal|fail' "$LOGFILE"; then
         fail "One or more errors in LOGFILE=$LOGFILE"
     fi
 fi