github actions: Add ciq-6.12.y-next and ciq-6.18.y-next to VALID_BASES

The automated CLK rebase workflow creates PRs against ciq-6.18.y-next
and ciq-6.12.y-next rather than the main CLK branches directly. These
-next branches are unique to CLK rebase and are not regular developer
branches, so they were not previously included in VALID_BASES. Add them
so the compare-results job recognizes them as valid PR targets.

Author: bmastbergen

.github/workflows/kernel-build-and-test-multiarch.yml

@@ -537,7 +537,7 @@ jobs:
 
         # Define whitelist of valid base branches
         # TODO: Use a centralized place to get the base branches
-        VALID_BASES="ciqlts9_2 ciqlts9_4 ciqlts8_6 ciqlts9_6 ciq-6.12.y ciq-6.18.y ciqcbr7_9"
+        VALID_BASES="ciqlts9_2 ciqlts9_4 ciqlts8_6 ciqlts9_6 ciq-6.12.y ciq-6.12.y-next ciq-6.18.y ciq-6.18.y-next ciqcbr7_9"
 
         echo "Current branch: $BRANCH_NAME"