Fixup gn_build.sh enable_qpg_builds=true after project-chip#7936 (pro…

…ject-chip#8091)

As of 2478e02 ("* Move naming qpg6100 to qpg (project-chip#7936)"), running

 ./gn_build.sh enable_qpg_builds=true

fails:

  ERROR at //BUILD.gn:340:16: Unable to load "/ssd/src/connectedhomeip5/config/qpg/toolchain/BUILD.gn".
        deps = [ "${chip_root}/examples/lock-app/qpg(${chip_root}/config/qpg/toolchain:qpg_lock_app)" ]
                 ^-----------------------------------------------------------------------------------

and furthermore that PR re-added it to debug builds where it doesn't
fit:

  ERROR at //examples/platform/qpg/args.gni:17:1: Value collision.
  import("${chip_root}/src/platform/qpg/args.gni")
  ^----------------------------------------------
  This import contains "is_debug"
  See //src/platform/qpg/args.gni:38:12: defined here.
  is_debug = false
             ^----
  Which would clobber the one in your current scope
  See //build/config/BUILDCONFIG.gn:17:14: defined here.
    is_debug = true
               ^---
  Executing import should not conflict with anything in the current
  scope unless the values are identical.
  See //examples/lock-app/qpg/args.gni:16:1: whence it was imported.
  import("${chip_root}/examples/platform/qpg/args.gni")
  ^---------------------------------------------------
  See //config/qpg/toolchain/BUILD.gn:23:5: whence it was imported.
      import("${chip_root}/examples/lock-app/qpg/args.gni")
      ^---------------------------------------------------
  See //BUILD.gn:340:16: which caused the file to be included.
        deps = [ "${chip_root}/examples/lock-app/qpg(${chip_root}/config/qpg/toolchain:qpg_lock_app)" ]
                 ^-----------------------------------------------------------------------------------

Rename the directory and remove it from debug builds again.

BUILD.gn

@@ -217,7 +217,7 @@ if (current_toolchain != "${dir_pw_toolchain}/default:default") {
     enable_efr32_lock_app_build = enable_efr32_builds
 
     # Build the qpgxxxx lock app example.
-    enable_qpg_lock_app_build = enable_qpg_builds
+    enable_qpg_lock_app_build = enable_qpg_builds && !is_debug
 
     # Build the efr32 lighting app example.
     enable_efr32_lighting_app_build = enable_efr32_builds