linux-purism-librem5: add pmb:kconfigcheck-librem5

Follow up to !5562 (merged), which introduced category:librem5. Add the related option, so CI actually enforces this category for the Librem 5.

[ci:skip-vercheck]: no need to rebuild for this

Depends on: pmbootstrap!2412 (merged)

.ci/lib/apkbuild_linting.py

@@ -23,9 +23,4 @@ if __name__ == "__main__":
         print("No APKBUILDs to lint")
         sys.exit(0)
 
-    result = common.run_pmbootstrap(["-q", "lint"] + packages, output_return=True)
-
-    if len(result) > 0:
-        print("Linting issues found:")
-        print(result)
-        sys.exit(1)
+    common.run_pmbootstrap(["-q", "lint"] + packages)