fix: replace grep -P with grep -E + sed for macOS compatibility in sync-compat.sh (#49127)

Author: Copilot

scripts/sync-compat.sh

@@ -33,7 +33,7 @@ for arg in "$@"; do
 done
 
 # Extract DefaultCopilotVersion from Go constants file
-COPILOT_VERSION=$(grep -oP '^\s*const DefaultCopilotVersion\s+Version\s*=\s*"\K[^"]+' "$CONSTANTS_FILE")
+COPILOT_VERSION=$(grep -E '^\s*const DefaultCopilotVersion' "$CONSTANTS_FILE" | sed -E 's/.*"([^"]+)".*/\1/')
 if [ -z "$COPILOT_VERSION" ]; then
   echo "Error: could not extract DefaultCopilotVersion from $CONSTANTS_FILE" >&2
   exit 1