Set Linux release builds to Ubuntu 20.04 (#64264)

Fix #64210

Linux release builds had been set to target ubuntu-latest. This picked
up ubuntu 22.10, which requires glibc 2.34, resulting in missing symbols
which prevented the game from running on the current, stable release of
other Linux distributions such as Debian 11.

Targeting ubutnu 20.04 should avoid breaking compatibility, and also
matches the OS settings configured for the rest of the build matrix.

.github/workflows/release.yml

@@ -116,7 +116,7 @@ jobs:
             content: application/zip
             sound: 1
           - name: Linux Tiles x64
-            os: ubuntu-latest
+            os: ubuntu-20.04
             mxe: none
             android: none
             tiles: 1
@@ -125,7 +125,7 @@ jobs:
             ext: tar.gz
             content: application/gzip
           - name: Linux Tiles Sounds x64
-            os: ubuntu-latest
+            os: ubuntu-20.04
             mxe: none
             android: none
             tiles: 1
@@ -134,7 +134,7 @@ jobs:
             ext: tar.gz
             content: application/gzip
           - name: Linux Curses x64
-            os: ubuntu-latest
+            os: ubuntu-20.04
             mxe: none
             android: none
             tiles: 0