doc: changelog: add modem_key_mgmt changes

Add new entry for race condition fix and move the fixes into their own
list as suggested by @peknis

Signed-off-by: Kamil Krzyzanowski <[email protected]>

Author: kamnxt

doc/nrf/releases_and_maturity/releases/release-notes-changelog.rst

@@ -559,7 +559,10 @@ Modem libraries
 
 * :ref:`modem_key_mgmt` library:
 
-  * Fixed an issue with the :c:func:`modem_key_mgmt_clear` function where it returned ``-ENOENT`` when the credential was cleared.
+  * Fixed:
+
+    * An issue with the :c:func:`modem_key_mgmt_clear` function where it returned ``-ENOENT`` when the credential was cleared.
+    * A race condition in several functions where ``+CMEE`` error notifications could be disabled by one function before the other one got a chance to run its command.
 
 * Updated the :ref:`nrf_modem_lib_lte_net_if` to automatically set the actual link :term:`Maximum Transmission Unit (MTU)` on the network interface when PDN connectivity is gained.