Fix: Use same libcurl variant as OpenVAS Scanner

Use libcurl in the GnuTLS flavor to have the same variant as used by the
OpenVAS Scanner install docs.

https://forum.greenbone.net/t/openvas-scanner-and-gvm-libs-dependencies-conflict/20115

.github/install-dependencies.sh

@@ -1,5 +1,5 @@
 #!/bin/sh
-# This script installs openvas-smb-dependencies.
+# This script installs gvm-libs dependencies
 set -ex
 apt-get update && \
   apt-get install -y --no-install-recommends \

INSTALL.md

@@ -47,7 +47,7 @@ Install prerequisites on Debian stable:
     apt-get install \
     cmake \
     libcjson-dev \
-    libcurl4-openssl-dev \
+    libcurl4-gnutls-dev \
     libgcrypt-dev \
     libglib2.0-dev \
     libgnutls28-dev \