ci: Update fetch-proxy to lookup versions by name (#12322)

We previously relied on knowing the tag structure, but this is brittle if we
change anything in the proxy repo. Instead, we now use the GitHub API to
list all releases, and we match the version by name.

.github/workflows/integration.yml

@@ -39,6 +39,7 @@ jobs:
             **/Dockerfile*
             charts/**
             justfile
+            bin/fetch-proxy
             bin/_test-helper.sh
           files_ignore: |
             .devcontainer/**

Dockerfile-proxy

@@ -19,7 +19,6 @@ COPY bin/fetch-proxy bin/fetch-proxy
 COPY bin/scurl bin/scurl
 ARG TARGETARCH
 ARG LINKERD2_PROXY_REPO="linkerd/linkerd2-proxy"
-ARG LINKERD2_PROXY_RELEASE_PREFIX="release/"
 ARG LINKERD2_PROXY_VERSION=""
 RUN --mount=type=secret,id=github \
     export GITHUB_TOKEN_FILE=/run/secrets/github; \

bin/docker-build-proxy

@@ -30,7 +30,6 @@ get_extra_options() {
 docker_build proxy "${TAG:-$(head_root_tag)}" "$dockerfile" \
   --build-arg LINKERD_VERSION="${TAG:-$(head_root_tag)}" \
   --build-arg LINKERD2_PROXY_REPO="${LINKERD2_PROXY_REPO:-linkerd/linkerd2-proxy}" \
-  --build-arg LINKERD2_PROXY_RELEASE_PREFIX="${LINKERD2_PROXY_RELEASE_PREFIX:-release/}" \
   --build-arg LINKERD2_PROXY_VERSION="${LINKERD2_PROXY_VERSION:-$(cat .proxy-version)}" \
   --secret id=github,env=LINKERD2_PROXY_GITHUB_TOKEN \
   $(get_extra_options)

bin/fetch-proxy

@@ -17,7 +17,6 @@ if [ -z "$proxy_repo" ]; then
 fi
 
 releases_url=https://api.github.com/repos/"$proxy_repo"/releases
-release_prefix="${LINKERD2_PROXY_RELEASE_PREFIX:-release/}"
 
 github_token="${GITHUB_TOKEN:-}"
 if [ -z "$github_token" ] && [ -n "${GITHUB_TOKEN_FILE:-}" ] && [ -f "$GITHUB_TOKEN_FILE" ]; then
@@ -37,10 +36,9 @@ cd "$builddir"
 
 version=${1:-latest}
 arch=${2:-amd64}
-tag="${release_prefix}${version}"
-release_url="$releases_url"/tags/"$(printf "$tag" | jq -sRr @uri)"
-if ! ghcurl "$release_url" > release.json ; then
-  echo "Failed to fetch $release_url" >&2
+
+if ! ghcurl "$releases_url" | jq '.[] | select(.name == "'"$version"'")' > release.json ; then
+  echo "Failed to fetch $releases_url" >&2
   exit 1
 fi