fix(get_config): use plain text GET for running/startup config

AOS-Switch returns the config body as text/plain, not JSON.
The previous get_config() called self.get() which calls resp.json(),
silently caught the JSONDecodeError, and returned ''. Now uses _get_text()
which reads resp.text directly.

napalm_procurve/api_client.py

@@ -435,15 +435,28 @@ class ProcurveApiClient:
         return result
 
     def get_config(self) -> Dict[str, str]:
-        """Return running and startup configuration via REST API."""
-        running = self.get("running-config")
-        startup = self.get("startup-config")
+        """Return running and startup configuration via REST API.
+
+        AOS-Switch returns the config as plain text, not JSON.
+        """
         return {
-            "running": running.get("config", ""),
-            "startup": startup.get("config", ""),
+            "running": self._get_text("running-config"),
+            "startup": self._get_text("startup-config"),
             "candidate": "",
         }
 
+    def _get_text(self, endpoint: str) -> str:
+        """GET *endpoint* and return the response body as plain text."""
+        url = self._base_url + endpoint
+        try:
+            resp = self._session.get(url, timeout=self.timeout)
+            if resp.ok:
+                return resp.text
+            logger.warning("GET %s returned HTTP %s: %s", url, resp.status_code, resp.text[:200])
+        except Exception as exc:
+            logger.warning("GET %s error: %s", url, exc)
+        return ""
+
     def get_ntp_servers(self) -> Dict[str, Dict]:
         """Return NTP servers from REST API."""
         data = self.get("ntp/server")