SCons: Enable wasm64 support on web builds

.github/workflows/web_builds.yml

@@ -20,16 +20,16 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - name: Template w/ threads (target=template_release, threads=yes)
+          - name: Template w/ threads, 64-bit (target=template_release, threads=yes, arch=wasm64)
             cache-name: web-template
             target: template_release
-            scons-flags: threads=yes
+            scons-flags: threads=yes arch=wasm64
             artifact: true
 
-          - name: Template w/o threads (target=template_release, threads=no)
+          - name: Template w/o threads, 32-bit (target=template_release, threads=no, arch=wasm32)
             cache-name: web-nothreads-template
             target: template_release
-            scons-flags: threads=no
+            scons-flags: threads=no arch=wasm32
             artifact: true
 
     steps: