Restore "-nightly" suffix to AppImage builds

The suffix is necessary to allow nightly builds to be installed
alongside release builds without conflicts. For example, it is
necessary for both builds to appear in:

- The system's application launcher menu.
- The file manager's right-click "Open with..." menu.
- The user's $PATH for command line usage.

build/ci/linux/build.sh

@@ -56,10 +56,6 @@ case "${BUILD_MODE}" in
 "mtests")        MUSESCORE_BUILD_CONFIG=dev; BUILDTYPE=installdebug; OPTIONS="USE_SYSTEM_FREETYPE=ON UPDATE_CACHE=FALSE PREFIX=$ARTIFACTS_DIR/software";;
 esac
 
-if [ "${BUILDTYPE}" == "portable" ]; then
-  SUFFIX="-portable${SUFFIX}" # special value needed for CMakeLists.txt
-fi
-
 echo "MUSESCORE_BUILD_CONFIG: $MUSESCORE_BUILD_CONFIG"
 echo "BUILD_NUMBER: $BUILD_NUMBER"
 echo "TELEMETRY_TRACK_ID: $TELEMETRY_TRACK_ID"

build/ci/linux/dumpsyms.sh

@@ -27,7 +27,7 @@ GEN_SCRIPT=tools/crashdump/generate_syms.sh
 ARTIFACTS_DIR=build.artifacts
 BUILD_DIR=build.release
 SYMBOLS_DIR=$ARTIFACTS_DIR/symbols
-MSCORE_BIN=$BUILD_DIR/src/main/mscore-portable
+MSCORE_BIN=$BUILD_DIR/src/main/mscore-portable*
 
 
 echo "GEN_SCRIPT: $GEN_SCRIPT"

ninja_build.sh

@@ -133,7 +133,7 @@ case $TARGET in
 
     appimage)
         MUSESCORE_INSTALL_DIR=MuseScore 
-        MUSESCORE_INSTALL_SUFFIX=-portable 
+        MUSESCORE_INSTALL_SUFFIX="-portable${MUSESCORE_INSTALL_SUFFIX}" # e.g. "-portable" or "-portable-nightly"
         MUSESCORE_LABEL="Portable AppImage" 
         MUSESCORE_NO_RPATH=ON 
 
@@ -146,7 +146,8 @@ case $TARGET in
         install_dir="$(cat $build_dir/PREFIX.txt)" 
         cd $install_dir
 
-        [ -L usr ] || ln -s . usr && mscore="mscore-portable" 
+        ln -sf . usr # we installed into the root of our AppImage but some tools expect a "usr" subdirectory
+        mscore="mscore${MUSESCORE_INSTALL_SUFFIX}"
         dsktp="${mscore}.desktop" 
         icon="${mscore}.svg" 
         mani="install_manifest.txt"