[roll] Roll fuchsia [codec][vaapi] Add const to copy assignment

llvm/llvm-project#89652 made
std::pair trivially copyable if its members are, and
it caused the following issue: "error: the parameter
for this explicitly-defaulted copy assignment operator
is const, but a member or base requires it to be
non-const". This patch adds const to copy assignment
operator to fix the issue.

Original-Bug: 354627057
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1086537
Original-Revision: 3d310ae50b6ea4982450cdb6f817fd2acfb02ead
GitOrigin-RevId: 25df2142c8e3b35418b44dc7ffa7afe524d0dd41
Change-Id: Ie60e29c2d9120a8dd6e1c1989e8451b6c7c45962

stem

@@ -11,7 +11,7 @@
              githooks="integration/git-hooks"
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="bef64e62b5009add35015f6240c3bcbbfd90f87c"/>
+             revision="3d310ae50b6ea4982450cdb6f817fd2acfb02ead"/>
   </projects>
   <hooks>
     <hook name="install-environment"