Update README, snap version, and tag

Author: github-actions[bot]

README.md

@@ -403,7 +403,7 @@ also often get polled from the printer.
   - pappl v1.4.9
   - qpdf v11.10.1
   - ghostscript ghostpdl-10.05.0-test-base-001
-  - cups v2.4.11
+  - cups v2.4.12
   - libcupsfilters 2.1.1
   - libppd 2.1.1
   - cups-filters 2.0.1

rockcraft.yaml

@@ -1,6 +1,6 @@
 name: ps-printer-app
 base: ubuntu@22.04
-version: '20240504-18'
+version: '20240504-19'
 summary: PostScript Printer Application
 description: |
   The PostScript Printer Application is a PAPPL (Printer Application Framework) based Printer Application
@@ -241,7 +241,7 @@ parts:
   cups:
     source: https://github.com/OpenPrinting/cups
     source-type: git
-    source-tag: 'v2.4.11'
+    source-tag: 'v2.4.12'
     source-depth: 1
 # ext:updatesnap
 #   version-format: