feat: update MbedTLS URL to v3.6.1

Signed-off-by: Ryan Everett <ryan.everett@arm.com>
Change-Id: I2fbd280c2ee0b9f7ffd57b8cb53437a6c35ea0a0
diff --git a/tf-a-builder.yaml b/tf-a-builder.yaml
index d3ab7bb..601e36a 100644
--- a/tf-a-builder.yaml
+++ b/tf-a-builder.yaml
@@ -53,7 +53,7 @@
             default: 'http://releases.linaro.org/openembedded/aarch64/17.01/linaro-image-minimal-genericarmv8-20170127-888.rootfs.tar.gz'
         - string:
             name: MBEDTLS_URL
-            default: 'https://github.com/Mbed-TLS/mbedtls/archive/mbedtls-3.6.0.tar.gz'
+            default: 'https://github.com/Mbed-TLS/mbedtls/archive/mbedtls-3.6.1.tar.gz'
         - string:
             name: GERRIT_PATCHSET_NUMBER
             default: ''