[Nightly] Trigger image build for nightly (#5547)

### What this PR does / why we need it?
We should also trigger image build when nightly test related files are
changed to ensure the image is valid for nightly tests. Please note that
this only applies to image with the tag `main*`(which means build
triggered by PR).
### Does this PR introduce _any_ user-facing change?

### How was this patch tested?

- vLLM version: v0.13.0
- vLLM main:
7157596103

Signed-off-by: wangli <wangli858794774@gmail.com>

.github/workflows/pr_tag_image_build_and_push.yaml

@@ -26,6 +26,8 @@ on:
       - 'cmake/**'
       - 'CMakeLists.txt'
       - 'csrc/**'
+      # We should also trigger image build when nightly test related files are changed to ensure the image is valid for nightly tests
+      - 'tests/e2e/nightly/'
     types: [ labeled ]
   push:
     # Publish image when tagging, the Dockerfile in tag will be build as tag image