Add -misc-const-correctness to .clang-tidy

I keep getting suggestions from clangd to add 'const' to a bunch of local variables, which is not LLVM's style. This suppresses those.

Reviewed By: kadircet, aaron.ballman

Differential Revision: https://reviews.llvm.org/D131414

.clang-tidy

@@ -1,4 +1,4 @@
-Checks: '-*,clang-diagnostic-*,llvm-*,misc-*,-misc-unused-parameters,-misc-non-private-member-variables-in-classes,-misc-no-recursion,readability-identifier-naming'
+Checks: '-*,clang-diagnostic-*,llvm-*,misc-*,-misc-const-correctness,-misc-unused-parameters,-misc-non-private-member-variables-in-classes,-misc-no-recursion,readability-identifier-naming'
 CheckOptions:
   - key:             readability-identifier-naming.ClassCase
     value:           CamelCase