[Clang] Fix typo in is_replaceable diagnostic (llvm#144247)

Adjustment to llvm#143265; `because it not` should be `because it is not`.

Author: rkirsling

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -1779,7 +1779,7 @@ def note_unsatisfied_trait_reason
            "%HasArcLifetime{has an ARC lifetime qualifier}|"
            "%VLA{is a variably-modified type}|"
            "%VBase{has a virtual base %1}|"
-           "%NotScalarOrClass{not %select{a|an array of objects of}1 scalar or "
+           "%NotScalarOrClass{is not %select{a|an array of objects of}1 scalar or "
            "class type}|"
            "%NTRBase{has a non-trivially-relocatable base %1}|"
            "%NTRField{has a non-trivially-relocatable member %1 of type %2}|"

clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp

@@ -166,7 +166,7 @@ static_assert(__builtin_is_replaceable(const volatile int));
 static_assert(__builtin_is_replaceable(void()));
 // expected-error@-1 {{static assertion failed due to requirement '__builtin_is_replaceable(void ())}} \
 // expected-note@-1 {{'void ()' is not replaceable}} \
-// expected-note@-1 {{because it not a scalar or class type}}
+// expected-note@-1 {{because it is not a scalar or class type}}
 
 struct B {
  virtual ~B();