doc: release: 4.0: Add nanopb 0.4.9 update

Add section for nanopb and upstream sync.

(cherry picked from commit 373ed89)

Original-Signed-off-by: Pieter De Gendt <pieter.degendt@basalte.be>
GitOrigin-RevId: 373ed89
Cr-Build-Id: 8731572062094510337
Cr-Build-Url: https://cr-buildbucket.appspot.com/build/8731572062094510337
Copybot-Job-Name: zephyr-main-copybot-downstream
Change-Id: I2fd917069c05ae0d081f1b59cd350cc480b2b114
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/6008707
Reviewed-by: Al Semjonovs <asemjonovs@google.com>
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>
Tested-by: Al Semjonovs <asemjonovs@google.com>
Commit-Queue: Al Semjonovs <asemjonovs@google.com>

doc/releases/release-notes-4.0.rst

@@ -1071,6 +1071,12 @@ Trusted Firmware-M (TF-M)
 * TF-M was updated to version 2.1.1 (from 2.1.0).
   The release notes can be found at: https://trustedfirmware-m.readthedocs.io/en/tf-mv2.1.1/releases/2.1.1.html
 
+Nanopb
+******
+
+* Updated the nanopb module to version 0.4.9.
+  Full release notes at https://github.com/nanopb/nanopb/blob/0.4.9/CHANGELOG.txt
+
 LVGL
 ****