feat(tls): Implement AsMut for Certificate #2363

Job	Run time
rustfmt	6s
cargo-deny check	22s
check (ubuntu-latest)	1m 22s
codegen	19s
check (macOS-latest)	3m 47s
Check MSRV	1m 7s
check (windows-latest)	2m 55s
Interop Tests (ubuntu-latest)	37s
test (ubuntu-latest)	3m 5s
Interop Tests (macOS-latest)	1m 39s
test (macOS-latest)	6m 20s
Interop Tests (windows-latest)	2m 27s
Check unused dependencies (ubuntu-latest)	3m 52s
test (windows-latest)	4m 10s
Check unused dependencies (macOS-latest)	6m 46s
Check unused dependencies (windows-latest)	6m 16s
	45m 10s

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