fix(android): pin ndk version and repair build

While there, ensure we build Android and iOS also in release
branches. So we notice issues _before_ releasing.

.github/workflows/android.yml

@@ -3,6 +3,7 @@ on:
   push:
     branches:
       - mobile-staging
+      - 'release/**'
 jobs:
   test:
     runs-on: macos-latest
@@ -12,7 +13,8 @@ jobs:
           go-version: "1.14"
       - uses: actions/checkout@v2
       - run: brew cask install android-sdk
-      - run: echo y | sdkmanager --install "platforms;android-29" ndk-bundle
+      - run: echo y | sdkmanager --install "platforms;android-29"
+      - run: echo y | sdkmanager --install "ndk;21.3.6528147"
       - run: ./build-android.bash
         env:
           ANDROID_HOME: /usr/local/Caskroom/android-sdk/4333796

.github/workflows/ios.yml

@@ -3,6 +3,7 @@ on:
   push:
     branches:
       - mobile-staging
+      - 'release/**'
 jobs:
   test:
     runs-on: macos-latest

build-android.bash

@@ -11,7 +11,7 @@ if [ -z "$ANDROID_HOME" -o "$1" = "--help" ]; then
     echo ""
     echo "Then make sure you install the required packages:"
     echo ""
-    echo "sdkmanager --install 'build-tools;29.0.3' ndk-bundle"
+    echo "sdkmanager --install 'build-tools;29.0.3' 'ndk;21.3.6528147'"
     echo ""
     echo "or, if you already installed, that you're up to date:"
     echo ""
@@ -22,6 +22,28 @@ if [ -z "$ANDROID_HOME" -o "$1" = "--help" ]; then
     echo ""
     exit 1
 fi
+if [ -d $ANDROID_HOME/ndk-bundle ]; then
+    echo ""
+    echo "FATAL: currently we need 'ndk;21.3.6528147' instead of ndk-bundle"
+    echo ""
+    echo "See https://github.com/ooni/probe-engine/issues/1179."
+    echo ""
+    echo "To fix: sdkmanager --uninstall ndk-bundle"
+    echo ""
+    exit 1
+fi
+export ANDROID_NDK_HOME=$ANDROID_HOME/ndk/21.3.6528147
+if [ ! -d $ANDROID_NDK_HOME ]; then
+    echo ""
+    echo "FATAL: currently we need 'ndk;21.3.6528147'"
+    echo ""
+    echo "See https://github.com/ooni/probe-engine/issues/1179."
+    echo ""
+    echo "To fix: sdkmanager --install 'ndk;21.3.6528147'"
+    echo ""
+    exit 1
+fi
+
 topdir=$(cd $(dirname $0) && pwd -P)
 set -x
 export PATH=$(go env GOPATH)/bin:$PATH