CICD: Improve the GitHub Actions for Linux.

Do a few things:
- add a build for Debian trixie (as discussed in #4182);
- add a build for Ubuntu 24.04;
- rename the build definitions to match the build names;
- update the artifact uploads to use a non-deprecated version of the
  action, and name the artifact appropriately;
- remove a stale workflow file.

Signed-off-by: Michael Keller <github@ike.ch>

.github/workflows/scripts/linux-snap.patch

@@ -0,0 +1,44 @@
+diff --git a/snap/snapcraft.yaml b/snap/snapcraft.yaml
+index 9f34d0169..0d5a89fd9 100644
+--- a/snap/snapcraft.yaml
++++ b/snap/snapcraft.yaml
+@@ -35,6 +35,7 @@ parts:
+     source: https://github.com/Subsurface/googlemaps.git
+     plugin: make
+     build-packages:
++    - ccache
+     - qtbase5-dev
+     - wget
+     override-pull: |
+@@ -79,6 +80,7 @@ parts:
+     override-build: |
+       qmake \
+         INCLUDEPATH+=${CRAFT_PART_SRC}/QtHeaders \
++        CONFIG+=ccache \
+         ${CRAFT_PART_SRC}
+       craftctl default
+ 
+@@ -111,7 +113,11 @@ parts:
+     source: .
+     source-type: git
+     source-subdir: libdivecomputer
++    autotools-configure-parameters:
++    - CC="ccache gcc"
++    - CXX="ccache g++"
+     build-packages:
++    - ccache
+     - libbluetooth-dev
+     - libhidapi-dev
+     - libusb-dev
+@@ -134,8 +140,11 @@ parts:
+     - -DFTDISUPPORT=ON
+     - -DLIBDIVECOMPUTER_LIBRARIES=../../../stage/usr/local/lib/libdivecomputer.so
+     - -DLIBDIVECOMPUTER_INCLUDE_DIR=../../../stage/usr/local/include
++    - -DCMAKE_C_COMPILER_LAUNCHER=ccache
++    - -DCMAKE_CXX_COMPILER_LAUNCHER=ccache
+     build-packages:
+     - build-essential
++    - ccache
+     - libcurl4-gnutls-dev
+     - libftdi1-dev
+     - libgit2-dev