distro-dependencies: use "libgcrypt20-dev" instead of "libgcrypt-dev" (which does not exist)

The "libgcrypt-dev" package unfortunately does not exist in Debian or (K)Ubuntu (as anyone can see 1, 2).

When trying to build Plasma 6 without the package "libgcrypt20-dev", this was seen:

    CMake Error at /usr/share/cmake-3.28/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
    Could NOT find LibGcrypt (missing: LIBGCRYPT_LIBRARY LIBGCRYPT_INCLUDE_DIR)
    (Required is at least version "1.5.0")

After executing:

    $ dpkg -l | grep -i gcrypt
    ii  libgcrypt20:amd64                                        1.10.3-2build1                              amd64        LGPL Crypto library - runtime library
    ii  libssh-gcrypt-4:amd64                                    0.10.6-2build2                              amd64        tiny C SSH library (gcrypt flavor)
    $ sudo apt install -y libgcrypt20-dev        

the compilation continued.

Notes:

• To see similar packages, that page and that one can be seen.
• This merge request is very similar to that one.