ghactions: Build release artifacts on tag push

To be able to attach properly versioned binaries to our releases,
they need to be built after the git tag has been pushed.
This PR adds a new release.yml job for this.

Signed-off-by: Christophe Fergeau <[email protected]>

.github/workflows/release.yml

@@ -0,0 +1,37 @@
+name: Release build
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+jobs:
+  build:
+    runs-on: ubuntu-20.04 # explicitly use 20.04, see commit 428c40018a
+    timeout-minutes: 30
+    strategy:
+      fail-fast: false
+    steps:
+    - name: Checkout source code
+      uses: actions/checkout@v4
+      with:
+        fetch-depth: 1
+
+    - name: >-
+        WORKAROUND: Fetch tags that points to the revisions
+        checked-out(actions/checkout#1467)
+      run: |-
+        git fetch --tags --force
+
+    - name: Set up Go
+      uses: actions/setup-go@v3
+
+    - name: Build
+      run: |
+        make cross qemu-wrapper vm win-gvproxy win-sshproxy
+        mv bin/gvproxy.exe bin/gvproxy-windowsgui.exe
+
+    - uses: actions/upload-artifact@v3
+      with:
+        name: gvisor-tap-vsock-binaries
+        path: bin/*