Help: Use captions for code snippets in the `FetchContent` module

Instead of "manually" added captions use the Sphinx option of
`code-block` directive.

Modules/FetchContent.cmake

@@ -923,9 +923,8 @@ it depends directly on projects ``projB`` and ``projC``.  Both ``projB`` and
 that all five projects are available on a company git server.  The
 ``CMakeLists.txt`` of each project might have sections like the following:
 
-*projA*:
-
 .. code-block:: cmake
+  :caption: *projA*
 
   include(FetchContent)
   FetchContent_Declare(
@@ -952,9 +951,9 @@ that all five projects are available on a company git server.  The
   # Order is important, see notes in the discussion further below
   FetchContent_MakeAvailable(projD projB projC)
 
-*projB*:
 
 .. code-block:: cmake
+  :caption: *projB*
 
   include(FetchContent)
   FetchContent_Declare(
@@ -970,9 +969,9 @@ that all five projects are available on a company git server.  The
 
   FetchContent_MakeAvailable(projD projE)
 
-*projC*:
 
 .. code-block:: cmake
+  :caption: *projC*
 
   include(FetchContent)
   FetchContent_Declare(
@@ -1058,9 +1057,8 @@ firmware tarball using CMake's :manual:`script mode <cmake(1)>`.  The call to
 unpacked firmware will be placed in a ``firmware`` directory below the
 current working directory.
 
-*getFirmware.cmake*:
-
 .. code-block:: cmake
+  :caption: :file:`getFirmware.cmake`
 
   # NOTE: Intended to be run in script mode with cmake -P
   include(FetchContent)