android: fix clean build (#499)

updates tailscale/corp#17686

'make clean' will now purge the cached toolchain to ensure you're using the
right go version when switching branches.  make clean is run in CI before
building anything and the docker container name is updated to pick that up.

Signed-off-by: Jonathan Nobels <jonathan@tailscale.com>

Makefile

@@ -8,7 +8,9 @@
 # The docker image to use for the build environment.  Changing this
 # will force a rebuild of the docker image.  If there is an existing image
 # with this name, it will be used.
-DOCKER_IMAGE=tailscale-android-build-amd64-go1.23
+#
+# The convention here is tailscale-android-build-amd64-<date>
+DOCKER_IMAGE=tailscale-android-build-amd64-120924
 export TS_USE_TOOLCHAIN=1
 
 DEBUG_APK=tailscale-debug.apk
@@ -274,7 +276,11 @@ docker-remove-shell-image: ## Removes all docker shell image
 
 .PHONY: clean
 clean: ## Remove build artifacts.  Does not purge docker build envs.  Use dockerRemoveEnv for that.
-	-rm -rf android/build $(DEBUG_APK) $(RELEASE_AAB) $(RELEASE_TV_AAB) $(LIBTAILSCALE) android/libs *.apk *.aab
+clean: ## Remove build artifacts.  Does not purge docker build envs.  Use dockerRemoveEnv for that.
+	@echo "Cleaning up old build artifacts"
+	-rm -rf android/build $(DEBUG_APK) $(RELEASE_AAB) $(RELEASE_TV_AAB) $(LIBTAILSCALE) android/libs *.apk *.aab 
+	@echo "Cleaning cached toolchain"
+	-rm -rf $(HOME)/.cache/tailscale-go
 	-pkill -f gradle
 
 .PHONY: help

docker/DockerFile.amd64-build

@@ -42,5 +42,5 @@ COPY android/gradle android/gradle
 RUN ./android/gradlew
 
 # Build the android app, bump the playstore version code, and make the tv release
-CMD make release && make bump_version_code && make release-tv
+CMD make clean && make release && make bump_version_code && make release-tv