internal/civisibility: fix RWMutex usages (#2982) #3347

Job	Run time
Prepare Go modules cache	7s
Smoke Tests / Test matrix	2s
macos-latest (AppSec disabled)	2m 7s
macos-12 go1.23	5m 59s
windows-latest (AppSec disabled)	3m 32s
macos-12 go1.22	7m 20s
ubuntu-latest-16-cores (AppSec disabled)	1m 26s
linux/amd64 golang:1.23-bookworm	1m 32s
macos-14 go1.23	5m 7s
linux/arm64 golang:1.23-bookworm	3m 22s
macos-14 go1.22	4m 21s
linux/amd64 golang:1.23-bullseye	1m 34s
linux/arm64 golang:1.23-bullseye	3m 19s
linux/amd64 golang:1.23-alpine	1m 30s
linux/arm64 golang:1.23-alpine	2m 57s
linux/amd64 golang:1.22-bookworm	1m 32s
linux/arm64 golang:1.22-bookworm	3m 1s
linux/amd64 golang:1.22-bullseye	1m 30s
linux/arm64 golang:1.22-bullseye	3m 18s
linux/amd64 golang:1.22-alpine	1m 29s
linux/arm64 golang:1.22-alpine	3m 2s
Smoke Tests / Build go-dvwa (1.22, alpine, base)	1m 20s
Smoke Tests / Build go-dvwa (1.22, alpine, vendoring)	1m 5s
Smoke Tests / Build go-dvwa (1.22, debian, base)	1m 8s
Smoke Tests / Build go-dvwa (1.22, debian, vendoring)	1m 9s
Smoke Tests / Build go-dvwa (1.23, alpine, base)	1m 6s
Smoke Tests / Build go-dvwa (1.23, alpine, vendoring)	1m 9s
Smoke Tests / Build go-dvwa (1.23, debian, base)	1m 9s
Smoke Tests / Build go-dvwa (1.23, debian, vendoring)	1m 6s
	1h 7m 19s

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