fix generate-jwt.sh for zsh users (#4769)

.gitignore

@@ -39,3 +39,6 @@ db-tools/
 
 # Coverage report
 lcov.info
+
+# Generated by ./etc/generate-jwt.sh
+jwttoken/

etc/generate-jwt.sh

@@ -1,3 +1,4 @@
+#!/bin/bash
 # Borrowed from EthStaker's prepare for the merge guide
 # See https://github.com/remyroy/ethstaker/blob/main/prepare-for-the-merge.md#configuring-a-jwt-token-file
 
@@ -8,4 +9,4 @@ then
   openssl rand -hex 32 | tr -d "\n" | tee > ${SCRIPT_DIR}/jwttoken/jwt.hex
 else
   echo "${SCRIPT_DIR}/jwttoken/jwt.hex already exists!"
-fi
+fi