python: fix broken usage of FindPython.cmake breaking python selection

In commit 9a9a262ea1 we moved from
pkg-config to find_package() to work around a deficiency in the pkgsrc
package manager, which does not ship pkg-config files as intended by
CPython. In the process, Gentoo and other platforms that, unlike pkgsrc,
publicly support multiple versions of python installed in parallel, had
python version selection broken. Consequently, weechat linked to the
wrong python, which happened to be installed in build chroots but was
not the versioned python package that the weechat package listed as a
dependency. Attempting to install weechat then broke on some systems
(which installed one version of python as a dependency but actually
linked to a totally different one).

This happens due to a design bug in upstream CMake. It is never
conceptually reasonable to use

```
find_package(Python COMPONENTS ...)
```

and omit the "Interpreter" component; if you do, CMake will ignore its
own documentation on how to control the build to use a specific python,
and choose one randomly (== "latest version available"). If, and only
if, the Interpreter component is checked, the development headers /
libraries for python will be guaranteed consistent with the documented
lookup variables from FindPython.cmake's documentation.

Bug: https://bugs.gentoo.org/968814
Fixes: 9a9a262ea1
Fixes: https://github.com/weechat/weechat/pull/2251
Signed-off-by: Eli Schwartz <eschwartz@gentoo.org>

src/plugins/python/CMakeLists.txt

@@ -20,9 +20,9 @@
 #
 
 if(CMAKE_VERSION VERSION_LESS "3.18.0")
-  find_package(Python 3.0 REQUIRED COMPONENTS Development)
+  find_package(Python 3.0 REQUIRED COMPONENTS Interpreter Development)
 else()
-  find_package(Python 3.0 REQUIRED COMPONENTS Development.Embed)
+  find_package(Python 3.0 REQUIRED COMPONENTS Interpreter Development.Embed)
 endif()
 
 add_library(python MODULE