GHA: Add Linux ARM toolchain

.github/actions/setup-linux-toolchain/action.yml

@@ -15,6 +15,9 @@ runs:
         TOOLCHAIN_64_SHA=16c8302fcb676c1f0fb9df73d6cff250ba1f4286
         TOOLCHAIN_32_URL=https://github.com/godotengine/buildroot/releases/download/godot-2020.11.x-2/i686-godot-linux-gnu_sdk-buildroot.tar.bz2
         TOOLCHAIN_32_SHA=6171652abc54ef219e5187bc53660ee4e2f796f4
+        TOOLCHAIN_ARM64_URL=https://github.com/godotengine/buildroot/releases/download/godot-2020.11.x-2/arm-godot-linux-gnueabihf_sdk-buildroot.tar.bz2
+        TOOLCHAIN_ARM64_SHA=72fd02826dfbcf2ad679d5fda0a4e6882a548fbd
+
         # ! Export variables:
         if [[ "${{ inputs.arch }}" == "x86_64" ]]; then
           echo "TOOLCHAIN_URL=${TOOLCHAIN_64_URL}" >> "$GITHUB_ENV"
@@ -22,6 +25,9 @@ runs:
         elif [[ "${{ inputs.arch }}" == "x86_32" ]]; then
           echo "TOOLCHAIN_URL=${TOOLCHAIN_32_URL}" >> "$GITHUB_ENV"
           echo "TOOLCHAIN_SHA=${TOOLCHAIN_32_SHA}" >> "$GITHUB_ENV"
+        elif [[ "${{ inputs.arch }}" == "arm64" ]]; then
+          echo "TOOLCHAIN_URL=${TOOLCHAIN_ARM64_URL}" >> "$GITHUB_ENV"
+          echo "TOOLCHAIN_SHA=${TOOLCHAIN_ARM64_SHA}" >> "$GITHUB_ENV"
         fi
 
     - name: Cache buildroot