ci(build): changes the base of the snap build to fix compatibility is…

…sues with GLIBC version

Changes base to core20 in an attempt to fix the error `node: /lib/x86_64-linux-gnu/libc.so.6:
version `GLIBC_2.28' not found (required by node)` during snap builds

snap/snapcraft.yaml

@@ -6,7 +6,7 @@ description: >
   Jellyseerr is a free and open source software application for managing requests for your media library.
   It is a a fork of Overseerr built to bring support for & focusing mainly on Jellyfin & Emby media servers!
   It integrates with your existing services such as Sonarr, Radarr, and Jellyfin/Emby/Plex.
-base: core18
+base: core20
 confinement: strict
 
 architectures: