Correct the GitHub Action environment variable reference

We should be using vars instead of env.

Signed-off-by: Remy Suen <remy.suen@docker.com>

Author: rcjsuen

.github/workflows/build.yml

@@ -265,7 +265,7 @@ jobs:
 
       - name: Build for ${{ matrix.os }}-${{ matrix.arch }}
         run: |
-          GOOS=${{ matrix.os }} GOARCH=${{ matrix.arch }} BUGSNAG_API_KEY=${{ secrets.BUGSNAG_API_KEY }} TELEMETRY_ENDPOINT=${{ env.TELEMETRY_ENDPOINT }} TELEMETRY_KEY=${{ secrets.TELEMETRY_KEY }} make build
+          GOOS=${{ matrix.os }} GOARCH=${{ matrix.arch }} BUGSNAG_API_KEY=${{ secrets.BUGSNAG_API_KEY }} TELEMETRY_ENDPOINT=${{ vars.TELEMETRY_ENDPOINT }} TELEMETRY_KEY=${{ secrets.TELEMETRY_KEY }} make build
 
       - name: Rename the binary to include the version number
         run: |