GHA: Update dependency Mbed-TLS/mbedtls to v3.6.1

Requires submodule checkout.

Change-Id: I86ceceb4e1c716b33c6c6ec8853eca0fb4b394f1
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Arne Schwabe <arne-openvpn@rfc2549.org>
Message-Id: <20240911144231.32553-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg29208.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

.github/workflows/build.yaml

@@ -404,9 +404,10 @@ jobs:
         uses: actions/checkout@v4
         with:
           path: mbedtls
+          submodules: true
           # versioning=semver-coerced
           repository: Mbed-TLS/mbedtls
-          ref: v3.5.2
+          ref: v3.6.1
       - name: "mbedtls: make no_test"
         run: make -j3 no_test SHARED=1
         working-directory: mbedtls