macOS: unable to get local issuer certificate

```
$ openssl s_server -accept 8443 -key certs/proxy.customs-key.pem -cert certs/proxy.customs.pem -www
Using auto DH parameters
Using default temp ECDH parameters
ACCEPT
4569913004:error:14037418:SSL routines:ACCEPT_SR_KEY_EXCH:tlsv1 alert unknown ca:/System/Volumes/Data/SWE/macOS/BuildRoots/533514bb11/Library/Caches/com.apple.xbs/Sources/libressl/libressl-75.60.3/libressl-2.8/ssl/ssl_pkt.c:1200:SSL alert number 48
4569913004:error:140370E5:SSL routines:ACCEPT_SR_KEY_EXCH:ssl handshake failure:/System/Volumes/Data/SWE/macOS/BuildRoots/533514bb11/Library/Caches/com.apple.xbs/Sources/libressl/libressl-75.60.3/libressl-2.8/ssl/ssl_pkt.c:951:
ACCEPT
```

```
$ curl "https://proxy.customs:8443"
curl: (60) SSL certificate problem: unable to get local issuer certificate
More details here: https://curl.se/docs/sslcerts.html

curl failed to verify the legitimacy of the server and therefore could not
establish a secure connection to it. To learn more about this situation and
how to fix it, please visit the web page mentioned above.
```

```
$ mkcert -install
The local CA is already installed in the system trust store! 👍
Warning: "certutil" is not available, so the CA can't be automatically installed in Firefox! ⚠️
Install "certutil" with "brew install nss" and re-run "mkcert -install" 👈
```

Mac keychain:

macOS: `12.2.1`
OpenSSL: `LibreSSL 2.8.3`
curl: `curl 7.79.1`
mkcert: `v1.4.3`