Add support for linux-aarch64 (Arm) builds

Adds 'linux-aarch64' as one of the possible build architectures. This
enables plugin builds on Arm machines running Linux.

Tested on an M1 Macbook Pro running Ubuntu 2022.04 in a Parallels VM

.github/scripts/.build.zsh

@@ -57,6 +57,7 @@ build() {
     macos-arm64
     macos-universal
     linux-x86_64
+    linux-aarch64
   )
   local -r -a _valid_configs=(Debug RelWithDebInfo Release MinSizeRel)
   if [[ ${host_os} == 'macos' ]] {

.github/scripts/.package.zsh

@@ -48,6 +48,7 @@ package() {
     macos-arm64
     macos-universal
     linux-x86_64
+    linux-aarch64
   )
   local -r -a _valid_configs=(Debug RelWithDebInfo Release MinSizeRel)
   local -r _usage="

buildspec.json

@@ -76,6 +76,9 @@
         },
         "linux-x86_64": {
             "qtVersion": 6
+        },
+        "linux-aarch64": {
+            "qtVersion": 6
         }
     },
     "name": "obs-plugintemplate",