Incorrect capitalisation of Mbed TLS in generated changelogs.
### Summary

Capitalisation of 'Mbed TLS' in the changelog created by assemble_changelog.py is not correct, its using 'mbed TLS' instead.

diff --git a/scripts/assemble_changelog.py b/scripts/assemble_changelog.py
index b742cc8ca..d27cc4713 100755
--- a/scripts/assemble_changelog.py
+++ b/scripts/assemble_changelog.py
@@ -122,7 +122,7 @@ class ChangelogFormat:
 class TextChangelogFormat(ChangelogFormat):
     """The traditional Mbed TLS changelog format."""
 
-    _unreleased_version_text = '= mbed TLS x.x.x branch released xxxx-xx-xx'
+    _unreleased_version_text = '= Mbed TLS x.x.x branch released xxxx-xx-xx'
     @classmethod
     def is_released_version(cls, title):
         # Look for an incomplete release date
['scripts/assemble_changelog.py']