Download binary with right arch (#118)

* Url based on arch 

Signed-off-by: Ludea <ludovicw35@hotmail.com>

* arm64 instead of aarch64 

Signed-off-by: Ludea <ludovicw35@hotmail.com>

* Default to amd64 

Signed-off-by: Ludea <ludovicw35@hotmail.com>

---------

Signed-off-by: Ludea <ludovicw35@hotmail.com>

ct.sh

@@ -80,18 +80,22 @@ install_chart_testing() {
     fi
 
     local arch
-    arch=$(uname -m)
+    if [[ $(uname -m) == "aarch64" ]]; then
+      arch=arm64
+    else
+      arch=amd64
+    fi
     local cache_dir="$RUNNER_TOOL_CACHE/ct/$version/$arch"
     local venv_dir="$cache_dir/venv"
 
     if [[ ! -d "$cache_dir" ]]; then
         mkdir -p "$cache_dir"
 
         echo "Installing chart-testing ${version}..."
-        CT_CERT=https://github.com/helm/chart-testing/releases/download/$version/chart-testing_${version#v}_linux_amd64.tar.gz.pem
-        CT_SIG=https://github.com/helm/chart-testing/releases/download/$version/chart-testing_${version#v}_linux_amd64.tar.gz.sig
+        CT_CERT=https://github.com/helm/chart-testing/releases/download/$version/chart-testing_${version#v}_linux_$arch.tar.gz.pem
+        CT_SIG=https://github.com/helm/chart-testing/releases/download/$version/chart-testing_${version#v}_linux_$arch.tar.gz.sig
 
-        curl --retry 5 --retry-delay 1 -sSLo ct.tar.gz "https://github.com/helm/chart-testing/releases/download/$version/chart-testing_${version#v}_linux_amd64.tar.gz"
+        curl --retry 5 --retry-delay 1 -sSLo ct.tar.gz "https://github.com/helm/chart-testing/releases/download/$version/chart-testing_${version#v}_linux_$arch.tar.gz"
         cosign verify-blob --certificate $CT_CERT --signature $CT_SIG \
           --certificate-identity "https://github.com/helm/chart-testing/.github/workflows/release.yaml@refs/heads/main" \
           --certificate-oidc-issuer "https://token.actions.githubusercontent.com" ct.tar.gz