Update deprecated TokenCache API usage

There was a place in `ManagedIdentityClient` where the `TokenCache.find`
method was still being used, leading to some deprecation warnings being
printed. This updates that to use `TokenCache.search`.

Signed-off-by: Paul Van Eck <paulvaneck@microsoft.com>

Author: pvaneck

msal/managed_identity.py

@@ -283,7 +283,7 @@ def acquire_token_for_client(
             ManagedIdentity.ID, "SYSTEM_ASSIGNED_MANAGED_IDENTITY")
         now = time.time()
         if not claims_challenge:  # Then attempt token cache search
-            matches = self._token_cache.find(
+            matches = self._token_cache.search(
                 self._token_cache.CredentialType.ACCESS_TOKEN,
                 target=[resource],
                 query=dict(