stylelint: Adjust rules to stylelint 15

Commit 6402df7 updated stylelint, but I foolishly didn't trigger the
/devel scenario in that PR. Drop the deprecated "indentation" rule and
suppress the `media-feature-range-notation` errors like we did in
cockpit-machines.

Also explicitly set `selector-not-notation`, as we use nontrivial
selectors like `:not(:last-child)`.

.stylelintrc.json

@@ -4,8 +4,6 @@
     "stylelint-use-logical-spec"
   ],
   "rules": {
-    "indentation": 2,
-
     "declaration-colon-newline-after": null,
     "selector-list-comma-newline-after": null,
 
@@ -26,6 +24,7 @@
     "function-url-quotes": null,
     "keyframes-name-pattern": null,
     "max-line-length": null,
+    "media-feature-range-notation": "prefix",
     "no-descending-specificity": null,
     "no-duplicate-selectors": null,
     "scss/at-extend-no-missing-placeholder": null,
@@ -38,6 +37,7 @@
     "scss/operator-no-unspaced": null,
     "selector-class-pattern": null,
     "selector-id-pattern": null,
+    "selector-not-notation": "simple",
     "liberty/use-logical-spec": "always"
   }
 }