Bump third_party/openthread/repo from `2aeb8b8` to `7bd3abd` #5524

Job	Run time
Build framework (macos-release, -sdk macosx -configuration Release)	14m 15s
Build framework (ios-release, -sdk iphoneos -configuration Release)	15m 56s
Build framework (tvos-debug, -sdk appletvos -configuration Debug)	8m 41s
Build framework (watchos-debug, -sdk watchos -configuration Debug)	20m 3s
Run framework tests (asan, -enableAddressSanitizer YES -enableUndefinedBehaviorSanitizer YES)	36m 21s
Run framework tests (tsan, -enableThreadSanitizer YES)	48m 4s
Run framework tests (leaks, ENABLE_LEAK_DETECTION=1)	34m 12s
	2h 57m 32s

Provide feedback