ci/android: Use structured tag for Android CTS version

Structured tagging ensures that we are building and testing the current
component version specified in the commit by matching the checksum of
the related build script file.

In this case, it is worthy to isolate the Android CTS version part,
because we don't need to rebuild the entire test-android container when
we change the CTS version or the CTS modules filtering.

PS: actually the new file `build-android-cts.sh` is not building
anything, it is just downloads, filters, compress and reupload the
stripped version to S3. The `build-` prefix is to make it work
transparently with `bin/ci/update_tag.py` script.

Signed-off-by: Guilherme Gallo <guilherme.gallo@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35596>

.gitlab-ci/test/gitlab-ci.yml

@@ -187,6 +187,10 @@ yaml-toml-shell-py-test:
     paths:
       - results/
 
+.test-android-cts:
+  variables:
+    ANDROID_CTS_TAG: ${CONDITIONAL_BUILD_ANDROID_CTS_TAG}
+
 .test-angle:
   variables:
     ANGLE_TAG: ${CONDITIONAL_BUILD_ANGLE_TAG}