Bump third_party/pigweed/repo from `9504c03` to `fbb318a` #1068

Job	Run time
REPL Tests - Linux	34m 33s
Test Suites - Darwin (no-ble-asan-clang)	1h 1m 31s
Test Suites - Darwin (no-ble-tsan-clang)	2h 3m 56s
Test Suites - Linux (no-ble-tsan-clang)	1h 50m 3s
REPL Tests - Darwin	0s
	5h 30m 3s

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