Include error with ntfy failure messages

Although it is undocumented, *ntfy* accepts a `Message` header along
with a file upload, which sets the message content of the notification
when a file is attached.  Since HTTP headers cannot contain multiple
lines, the newline character has to be escaped.  The *ntfy* server
performs unescaping automatically.

xactfetch.py

@@ -47,20 +47,22 @@ def ntfy(
     if tags:
         headers['Tags'] = tags
     url = f'{NTFY_URL}/{topic}'
-    if message:
-        r = requests.post(
-            url,
-            headers=headers,
-            data=message,
-        )
-    else:
+    if attach:
         if filename:
             headers['Filename'] = filename
+        if message:
+            headers['Message'] = message.replace('\n', '\\n')
         r = requests.put(
             url,
             headers=headers,
             data=attach,
         )
+    else:
+        r = requests.post(
+            url,
+            headers=headers,
+            data=message,
+        )
     r.raise_for_status()
 
 
@@ -269,6 +271,7 @@ class ntfyerror:
             if ss := self.page.screenshot():
                 save_screenshot(ss)
             ntfy(
+                message=str(exc_value),
                 title=f'xactfetch failed for {self.bank}',
                 tags='warning',
                 attach=ss,