Build system setup failure due to OS / Curl SSL Certificate Issues

Hi all,

It appears that sometime overnight, something has broken on the Travis CI Build Platform when setting up a basic x64 build. The main error that occurs is this:

e[0K$ __mirrors=(
    "https://dlang.org/install.sh"
    "https://nightlies.dlang.org/install.sh"
    "https://github.com/dlang/installer/raw/stable/script/install.sh"
  )
  for i in {0..4}; do
    for mirror in "${__mirrors[@]}" ; do
      if curl -fsSL -A "$CURL_USER_AGENT" --connect-timeout 5 --speed-time 30 --speed-limit 1024 "$mirror" -O ; then
        break 2
      fi
    done
    sleep $((1 << i))
  done
  unset __mirrors
  
curl: (60) server certificate verification failed. CAfile: /etc/ssl/certs/ca-certificates.crt CRLfile: none
More details here: http://curl.haxx.se/docs/sslcerts.html

curl performs SSL certificate verification by default, using a "bundle"
 of Certificate Authority (CA) public keys (CA certs). If the default
 bundle file isn't adequate, you can specify an alternate file
 using the --cacert option.
If this HTTPS server uses a certificate signed by a CA represented in
 the bundle, the certificate verification probably failed due to a
 problem with the certificate (it might be expired, or the name might
 not match the domain name in the URL).
If you'd like to turn off curl's verification of the certificate, use
 the -k (or --insecure) option.
curl: (28) Connection timed out after 5001 milliseconds
travis_time:end:0db3f330:start=1610317983189698097,finish=1610318002196900675,duration=19007202578,event=
e[0Ktravis_time:start:1f457991
e[0K$ source "$(CURL_USER_AGENT="$CURL_USER_AGENT" bash install.sh dmd --activate)"
curl: (60) server certificate verification failed. CAfile: /etc/ssl/certs/ca-certificates.crt CRLfile: none
More details here: http://curl.haxx.se/docs/sslcerts.html

Additional Information:

Any suggestions are greatly appreciated.

FYI to @MartinNowak and @wilzbach

Problem with the 3rd-party server(s), same as below but with different intermediate certificate(s) missing: SSL Server Test: dlang.org (Powered by Qualys SSL Labs) .