Add external/shaderc/spirv-headers to the manifest

Bug: 64265767
Test: repo sync

default.xml

@@ -287,6 +287,7 @@
   <project path="external/scrypt" name="platform/external/scrypt" groups="pdk" />
   <project path="external/seccomp-tests" name="platform/external/seccomp-tests" />
   <project path="external/selinux" name="platform/external/selinux" groups="pdk" />
+  <project path="external/shaderc/spirv-headers" name="platform/external/shaderc/spirv-headers" groups="pdk" />
   <project path="external/shflags" name="platform/external/shflags" groups="pdk" />
   <project path="external/sfntly" name="platform/external/sfntly" groups="pdk,qcom_msm8x26" />
   <project path="external/skia" name="platform/external/skia" groups="pdk,qcom_msm8x26" />