Compile CTS Bluetooth tests for both 32-bit and 64-bit.

Add `compile_multilib: "both",` to the Bluetooth test module to ensure
it is built for both 32-bit and 64-bit ABIs, which avoids
INSTALL_FAILED_NO_MATCHING_ABIS issue.

Bug: 443586643

Test: atest CtsBluetoothTestCases -- --abi x86

Flag: TEST_ONLY

Change-Id: I1f88f342b7d8d08f42d45e4b0cd3d71e7234696b