`-D IGNORE_VENDORED_DEPENDENCIES=ON`: "fmt::fmt-header-only" not found

With option `-D IGNORE_VENDORED_DEPENDENCIES=ON`, executing `cmake` fails although "fmt" is installed.

```sh
-- Found Boost headers in
-- Found Boost::filesystem at
-- Found Boost::unit_test_framework at
-- Found Boost::program_options at
-- Found Boost::system at
-- Performing Test fmacro-prefix-map=/home/matheus/programmieren/solidity=/solidity
-- Performing Test fmacro-prefix-map=/home/matheus/programmieren/solidity=/solidity - Success

------------------------------------------------------------------------
-- Configuring solidity 0.8.28
------------------------------------------------------------------------
--                  CMake Version                            3.31.5
-- CMAKE_BUILD_TYPE Build type                               None
-- TARGET_PLATFORM  Target platform                          Linux
--------------------------------------------------------------- features
-- COVERAGE         Coverage support                         OFF
------------------------------------------------------------- components
-- TESTS            Build tests                              ON
------------------------------------------------------------------ flags
-- OSSFUZZ                                                   OFF
------------------------------------------------------------------------

-- Found Z3: /usr/lib/cmake/z3/Z3Config.cmake (found version "4.13.4.0")
Z3 SMT solver found. This enables optional SMT checking with Z3.
-- Configuring done (0.6s)
CMake Error at libsolutil/CMakeLists.txt:49 (target_link_libraries):
  Target "solutil" links to:

    fmt::fmt-header-only

  but the target was not found.  Possible reasons include:

    * There is a typo in the target name.
    * A find_package call is missing for an IMPORTED target.
    * An ALIAS target is missing.



CMake Error at liblangutil/CMakeLists.txt:34 (target_link_libraries):
  Target "langutil" links to:

    fmt::fmt-header-only

  but the target was not found.  Possible reasons include:

    * There is a typo in the target name.
    * A find_package call is missing for an IMPORTED target.
    * An ALIAS target is missing.



CMake Error at libevmasm/CMakeLists.txt:46 (target_link_libraries):
  Target "evmasm" links to:

    fmt::fmt-header-only

  but the target was not found.  Possible reasons include:

    * There is a typo in the target name.
    * A find_package call is missing for an IMPORTED target.
    * An ALIAS target is missing.



CMake Error at libyul/CMakeLists.txt:202 (target_link_libraries):
  Target "yul" links to:

    fmt::fmt-header-only

  but the target was not found.  Possible reasons include:

    * There is a typo in the target name.
    * A find_package call is missing for an IMPORTED target.
    * An ALIAS target is missing.



CMake Error at libsolidity/CMakeLists.txt:222 (target_link_libraries):
  Target "solidity" links to:

    fmt::fmt-header-only

  but the target was not found.  Possible reasons include:

    * There is a typo in the target name.
    * A find_package call is missing for an IMPORTED target.
    * An ALIAS target is missing.



-- Generating done (0.3s)
CMake Generate step failed.  Build files cannot be regenerated correctly.
```

[]