ci: install Botan, which rnp needs

First run: all three jobs stopped at configure with

    Could NOT find Botan (missing: BOTAN_LIBRARY BOTAN_INCLUDE_DIR)

Botan is not a dependency of libretroshare -- it appears in none of its
find_package calls, which is why it was missing from these lists -- but rnp
requires it, and rnp is pulled in by FetchContent as soon as RS_RNPLIB is on.
The super-project's CIs install it for the same reason.

libbotan-2-dev, mingw-w64-ucrt-x86_64-libbotan, botan@2.

.github/workflows/macos-cmake.yml

@@ -49,7 +49,7 @@ jobs:
       run: >
         brew install
         cmake ninja pkg-config
-        openssl@3 sqlcipher miniupnpc json-c
+        openssl@3 botan@2 sqlcipher miniupnpc json-c
         bzip2 zlib doxygen
 
     - name: CMake configure

.github/workflows/ubuntu-cmake.yml

@@ -52,7 +52,7 @@ jobs:
         sudo apt-get update &&
         sudo apt-get install -y
         build-essential g++ cmake ninja-build pkg-config git
-        libssl-dev zlib1g-dev libbz2-dev libjson-c-dev
+        libssl-dev zlib1g-dev libbz2-dev libjson-c-dev libbotan-2-dev
         libsqlcipher-dev libminiupnpc-dev
         doxygen python3
 

.github/workflows/windows-cmake.yml

@@ -60,6 +60,7 @@ jobs:
             mingw-w64-ucrt-x86_64-python
             mingw-w64-ucrt-x86_64-doxygen
             mingw-w64-ucrt-x86_64-openssl
+            mingw-w64-ucrt-x86_64-libbotan
             mingw-w64-ucrt-x86_64-sqlcipher
             mingw-w64-ucrt-x86_64-miniupnpc
             mingw-w64-ucrt-x86_64-json-c