fix(regexp): escape leading digit (#6208) #100

Job	Run time
wasm (crypto/_wasm)	4s
test-node (latest, ubuntu-latest)	20s
lint (ubuntu-latest)	29s
test (v1.x, ubuntu-latest)	1m 31s
lint (windows-latest)	40s
test (v1.x, windows-latest)	1m 34s
test (v1.x, macOS-latest)	1m 23s
test (v2.x, ubuntu-latest)	2m 11s
test (v2.x, windows-latest)	2m 51s
test (v2.x, macOS-latest)	1m 56s
test (canary, ubuntu-latest)	2m 9s
test (canary, windows-latest)	2m 32s
test (canary, macOS-latest)	2m 0s
	19m 40s

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