Bump third_party/mbedtls/repo from `5bc604f` to `2153b1b` #2032

Job	Run time
REPL Tests - Linux	1h 30m 36s
Test Suites - Darwin (no-ble-asan-clang)	1h 40m 41s
Test Suites - Linux (no-ble-tsan-clang)	1h 49m 16s
Test Suites - Darwin (no-ble-tsan-clang)	1h 51m 2s
REPL Tests - Darwin	0s
	6h 51m 35s

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