Fix parentheses around assignment warning for GCC13

[nvmkuruc]

Description of Change(s)

OpenUSD/pxr/usd/usd/primDefinition.cpp

Line 408 in b8dbd19

if (destSpec = _composedPropertyLayer->GetObjectAtPath(

The previous line produces a warning on GCC13.

warning: suggest parentheses around assignment used as truth value [-Wparentheses]
  408 |         if (destSpec = (_composedPropertyLayer->GetObjectAtPath(
      |             ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  409 |                 primPath.AppendProperty(propName)))) {
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In #3334, @dgovil suggests this occurs on clang 16 too. Putting parentheses around the expression confirms that the assignment as truth value is intentional.

Link to proposal (if applicable)

Fixes Issue(s)

#3334

Checklist

• I have created this PR based on the dev branch

• I have followed the coding conventions

• I have added unit tests that exercise this functionality (Reference:
  testing guidelines)

• I have verified that all unit tests pass with the proposed changes

• I have submitted a signed Contributor License Agreement (Reference:
  Contributor License Agreement instructions)

[jesschimein]

Filed as internal issue #USD-11584

(This is an automated message. See here for more information.)