Tests

Bump third_party/pigweed/repo from `1f12d06` to `8512b20` #983

Job	Run time
REPL Tests - Darwin	0s
REPL Tests - Linux	1h 3m 26s
Test Suites - Darwin (no-ble-asan-clang)	2m 52s
Test Suites - Darwin (no-ble-tsan-clang)	2m 27s
Test Suites - Linux (no-ble-tsan-clang)	1h 35m 35s
	2h 44m 20s

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