stack/erp5: fix error detection and error message with repozo on py3

The syntax to compare strings is

      STRING1 = STRING2
                     True if the strings are equal.
      STRING1 != STRING2
                     True if the strings are not equal.

STRING1=STRING2 is not a valid syntax for strings comparisons.

This is same fix as 6cf1769d (ERP5: fix handling of repozo restoration
failure, 2024-10-24) and also a fix to a wrong error message, because
this is not restoration script, it's backup script.

stack/erp5/buildout.hash.cfg

@@ -78,7 +78,7 @@ md5sum = 1333d2fc21f64da4010a4eafea59d141
 
 [template-zeo]
 filename = instance-zeo.cfg.in
-md5sum = 6513f1ecd9a2daaf36ca720f15932ae3
+md5sum = 025f11aef75bf00d61e90c6734ce13d8
 
 [template-zeo-conf]
 filename = zeo.conf.in

stack/erp5/instance-zeo.cfg.in

@@ -108,9 +108,9 @@ inline =
     --file="$zodb_directory/$zodb_path"
 
   CURRENT_EXIT_CODE=$?
-  if [ ! "$CURRENT_EXIT_CODE"="0" ]; then
+  if [ $CURRENT_EXIT_CODE != 0 ]; then
     EXIT_CODE="$CURRENT_EXIT_CODE"
-    echo "$storage_name Backup restoration failed."
+    echo "$storage_name Backup failed."
   fi
   {%   endfor -%}
   {% endfor -%}