cleanup: define required Go version just once (#861)

See https://github.com/ooni/probe/issues/2217

.github/workflows/android.yml

@@ -14,14 +14,18 @@ jobs:
       contents: write
 
     steps:
-      - uses: actions/setup-go@v1
-        with:
-          go-version: "1.18.3"
-
       - uses: actions/checkout@v2
         with:
           fetch-depth: 0
 
+      - name: Get GOVERSION content
+        id: goversion
+        run: echo ::set-output name=version::$(cat GOVERSION)
+
+      - uses: actions/setup-go@v1
+        with:
+          go-version: "${{ steps.goversion.outputs.version }}"
+
       - run: |
           echo -n $PSIPHON_CONFIG_KEY > ./internal/engine/psiphon-config.key
           echo $PSIPHON_CONFIG_JSON_AGE_BASE64 | base64 -d > ./internal/engine/psiphon-config.json.age