ci: install x86_64-unknown-linux-gnu rust target for lsposed jobs

Gobley's cargo plugin enumerates Kotlin targets at gradle configure
time and queries rustup for each one — including the JVM host target,
even though we never build for it (`androidUnitTest = false` skips
wiring the JVM cargo build into Android unit tests, but the build
entry is still created at configure time).

Without `x86_64-unknown-linux-gnu` installed, that lookup returns
null and `:app:lint` / `assembleRelease` die with a bare
`NullPointerException` during project configuration.

Add the target as a workflow step in the lint and lsposed jobs so
this PR's CI passes immediately, and bake it into the CI Dockerfile
so subsequent image rebuilds carry it.

.github/docker/ci/Dockerfile

@@ -50,7 +50,7 @@ ENV RUSTUP_HOME=/usr/local/rustup \
 
 RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | \
         sh -s -- -y --default-toolchain stable --profile minimal --no-modify-path && \
-    rustup target add aarch64-linux-android && \
+    rustup target add aarch64-linux-android x86_64-unknown-linux-gnu && \
     rustup component add rustfmt clippy && \
     cargo install cargo-ndk --locked && \
     chmod -R a+w /usr/local/rustup /usr/local/cargo

.github/workflows/ci.yml

@@ -74,6 +74,11 @@ jobs:
       # Kotlin
       - name: ktlint
         run: ktlint "lsposed/**/*.kt"
+      # Gobley's cargo plugin enumerates Kotlin targets at gradle configure
+      # time and queries rustup for each, including the JVM host target.
+      # Without this target installed gradle dies with a NullPointerException.
+      - name: Add Linux x64 Rust target
+        run: rustup target add x86_64-unknown-linux-gnu
       - name: Android lint
         run: cd lsposed && ./gradlew --no-daemon :app:lint
       - name: Kotlin unit tests
@@ -201,6 +206,12 @@ jobs:
           storeFile=$KEYSTORE_PATH
           EOF
 
+      # Gobley's cargo plugin enumerates Kotlin targets at gradle configure
+      # time and queries rustup for each, including the JVM host target.
+      # Without this target installed gradle dies with a NullPointerException.
+      - name: Add Linux x64 Rust target
+        run: rustup target add x86_64-unknown-linux-gnu
+
       - name: Build APK
         run: |
           cd "$GITHUB_WORKSPACE/lsposed" && ./gradlew --no-daemon assembleRelease