Bump third_party/pigweed/repo from `1f12d06` to `46609c5` #950

Job	Run time
Build framework (macos-release, -sdk macosx -configuration Release)	2m 25s
Build framework (ios-release, -sdk iphoneos -configuration Release)	2m 41s
Build framework (tvos-debug, -sdk appletvos -configuration Debug)	2m 8s
Build framework (watchos-debug, -sdk watchos -configuration Debug)	2m 0s
Run framework tests	0s
	9m 14s

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