android: fixate api_level to be 29 (#918)

Fixing android's api to 29 since it seems like api 30 has some bazel proguard issues which are similar to: bazelbuild/bazel#3777

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Description: android: fixate api_level to be 29
Risk Level: low
Testing: ci
Docs Changes: n/a
Release Notes: n/a
[Optional Fixes #Issue]
[Optional Deprecated:]

Signed-off-by: JP Simard <jp@jpsim.com>

mobile/WORKSPACE

@@ -37,6 +37,7 @@ envoy_mobile_dependencies()
 load("@envoy_mobile//bazel:envoy_mobile_toolchains.bzl", "envoy_mobile_toolchains")
 envoy_mobile_toolchains()
 
-android_sdk_repository(name = "androidsdk")
+# Fixing to API 29 since proguard seems to be failing for 30+
+android_sdk_repository(name = "androidsdk", api_level = 29)
 
 android_ndk_repository(name = "androidndk")