build: remove release-1.18 from Renovate baseBranches

Signed-off-by: Jared Watts <[email protected]>

Author: jbw976

.github/renovate.json5

@@ -14,7 +14,6 @@
   // PLEASE UPDATE THIS WHEN RELEASING.
   "baseBranches": [
     'main',
-    'release-1.18',
     'release-1.19',
     'release-1.20',
     'release-2.0',