ci(pip-build): respect disable-build-* labels for ubuntu / macos

`test-pip-build` (the workflow_call into pip-build.yml) ignored the
`disable-build-<platform>` PR labels and always tried to run the full
manylinux + macOS matrix. That bit PR #6090: a `disable-build-linux-vcpkg`
label suppressed the prepare-image step, but `test-pip-build` still tried to
pull the branch-tagged Rocky Linux image and failed with `manifest unknown`.

Plumb three new boolean inputs through pip-build.yml --
`disable_ubuntu_x64`, `disable_ubuntu_arm64`, `disable_macos` -- and gate
the matching build/test jobs:

- manylinux-pip-build / manylinux-pip-test: per-platform `if:` keyed on
  `matrix.platform` so x86_64 and aarch64 can be disabled independently
  (matches the `disable-build-ubuntu-{x64,arm64}` split elsewhere).
- macos-pip-build / macos-pip-test: single `if:` gated on `disable_macos`
  (both x86 and arm64 macOS variants together, matching the single
  `disable-build-macos` label).

`build-test-distribute.yml` derives the three flags from the same
`build_enable_<platform>` outputs that `prepare-image` already uses on the
adjacent line.

Out of scope (not requested): `disable-build-windows` (windows-pip-build
keeps running) and `disable-build-emscripten` (pip-build.yml has no
emscripten target).

Author: Fedr

.github/workflows/build-test-distribute.yml

@@ -318,6 +318,11 @@ jobs:
     uses: ./.github/workflows/pip-build.yml
     with:
       vcpkg_docker_image_tag: ${{ needs.config.outputs.vcpkg_docker_image_tag }}
+      # Honor `disable-build-<platform>` PR labels so test-pip-build skips the
+      # same platforms as the rest of CI.
+      disable_ubuntu_x64:   ${{ needs.config.outputs.build_enable_ubuntu_x64 != 'true' }}
+      disable_ubuntu_arm64: ${{ needs.config.outputs.build_enable_ubuntu_arm64 != 'true' }}
+      disable_macos:        ${{ needs.config.outputs.build_enable_macos != 'true' }}
 
   collect-stats:
     timeout-minutes: 5

.github/workflows/pip-build.yml

@@ -31,6 +31,18 @@ on:
         default: false
         required: false
         type: boolean
+      disable_ubuntu_x64:
+        default: false
+        required: false
+        type: boolean
+      disable_ubuntu_arm64:
+        default: false
+        required: false
+        type: boolean
+      disable_macos:
+        default: false
+        required: false
+        type: boolean
 
 env:
   VCPKG-VERSION: '2026.03.18'
@@ -57,6 +69,12 @@ jobs:
 
   manylinux-pip-build:
     needs: setup
+    # Skip per-platform when the caller passes the matching disable_* flag.
+    # `disable-build-ubuntu-x64` / `disable-build-ubuntu-arm64` PR labels in
+    # `build-test-distribute.yml` map to these inputs.
+    if: |
+      (matrix.platform == 'x86_64' && inputs.disable_ubuntu_x64 != true) ||
+      (matrix.platform == 'aarch64' && inputs.disable_ubuntu_arm64 != true)
     timeout-minutes: 80
     runs-on: ${{ matrix.runner }}
     container:
@@ -358,6 +376,7 @@ jobs:
 
   macos-pip-build:
     needs: setup
+    if: ${{ inputs.disable_macos != true }}
     timeout-minutes: 120
     runs-on: ${{ matrix.instance }}
     strategy:
@@ -448,6 +467,9 @@ jobs:
 
   manylinux-pip-test:
     needs: [manylinux-pip-build]
+    if: |
+      (matrix.platform == 'x86_64' && inputs.disable_ubuntu_x64 != true) ||
+      (matrix.platform == 'aarch64' && inputs.disable_ubuntu_arm64 != true)
     timeout-minutes: 20
     runs-on: ${{ matrix.runner }}
     container:
@@ -571,6 +593,7 @@ jobs:
 
   macos-pip-test:
     needs: [macos-pip-build]
+    if: ${{ inputs.disable_macos != true }}
     timeout-minutes: 40
     runs-on: ${{ matrix.instance }}
     strategy: