Bug 37850: (QA follow-up): Update illemail REST API attribute name

To test
1) yarn api:bundle && koha-plack --restart kohadev
2) Enable ILLModule and put some 'ILL staff email:' on some library
3) Access <staff_url>/api/v1/libraries
4) Notice the attribute reads ill_email

Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>

Koha/Library.pm

@@ -361,7 +361,7 @@ sub to_api_mapping {
         branchphone      => 'phone',
         branchfax        => 'fax',
         branchemail      => 'email',
-        branchillemail   => 'illemail',
+        branchillemail   => 'ill_email',
         branchreplyto    => 'reply_to_email',
         branchreturnpath => 'return_path_email',
         branchurl        => 'url',

api/v1/swagger/definitions/library.yaml

@@ -59,7 +59,7 @@ properties:
       - string
       - "null"
     description: the primary email address of the library
-  illemail:
+  ill_email:
     type:
       - string
       - "null"