Updated clang format style.

Author: luca-heltai

.clang-format

@@ -1,5 +1,5 @@
 #
-# The clang-format (Clang 11) style file used by deal.II.
+# The clang-format (Clang 16) style file used by deal.II.
 #
 
 AccessModifierOffset: -2
@@ -160,6 +160,8 @@ PointerAlignment: Right
 ReflowComments: true
 CommentPragmas: '( \| |\*--|<li>|@ref | @p |@param |@name |@returns |@warning |@ingroup |@author |@date |@related |@relates |@relatesalso |@deprecated |@image |@return |@brief |@attention |@copydoc |@addtogroup |@todo |@tparam |@see |@note |@skip |@skipline |@until |@line |@dontinclude |@include)'
 
+QualifierAlignment: Left
+
 SortIncludes: true
 SortUsingDeclarations: true
 
@@ -175,7 +177,7 @@ SpacesInContainerLiterals: false
 SpacesInParentheses: false
 SpacesInSquareBrackets: false
 
-Standard: Cpp11
+Standard: c++20
 
 TabWidth: 2