Update README, snap version, and tag

Author: github-actions[bot]

README.md

@@ -363,7 +363,7 @@ also often get polled from the printer.
   - qpdf v11.10.1
   - ghostscript ghostpdl-10.05.0-test-base-001
   - cups v2.4.11
-  - libcupsfilters 2.1.0
+  - libcupsfilters 2.1.1
   - libppd 2.1.0
   - pyppd release-1-1-0
   - hplip debian/3.22.10+dfsg0-8

rockcraft.yaml

@@ -1,6 +1,6 @@
 name: hplip-printer-app
 base: ubuntu@22.04
-version: '3.22.10-17'
+version: '3.22.10-18'
 summary: HPLIP Printer Application
 description: |
   The HPLIP Printer Application is a PAPPL (Printer Application
@@ -346,7 +346,7 @@ parts:
   libcupsfilters:
     source: https://github.com/OpenPrinting/libcupsfilters
     source-type: git
-    source-tag: '2.1.0'
+    source-tag: '2.1.1'
     source-depth: 1
 # ext:updatesnap
 #   version-format: