Cannot modify font used to render charts

Bug category

[ ] bug - compilation error
[ ] bug - compilation warning
[x] bug - runtime error
[ ] bug - runtime warning
[ ] bug - logic error

Describe the bug The font cannot be modified, and on Windows compiled with MinGW64 it incorrectly sets Helvetica and doesn't render any text in the affected charts (pie chart, word cloud, etc).

Steps to Reproduce

    auto ax = figure->current_axes ();
    ax->font ("Hack");
    figure->save (path, "png");

# Your steps go here
make build -j8

Output

```console gdImageStringFT: fontconfig: Didn't find expected font family. Perhaps URW Type 1 fonts need installing? while printing string Larry with font Helvetica gdImageStringFT: fontconfig: Didn't find expected font family. Perhaps URW Type 1 fonts need installing? while printing string Wendy with font Helvetica gdImageStringFT: fontconfig: Didn't find expected font family. Perhaps URW Type 1 fonts need installing? while printing string Iggy with font Helvetica gdImageStringFT: fontconfig: Didn't find expected font family. Perhaps URW Type 1 fonts need installing? while printing string Roy with font Helvetica gdImageStringFT: fontconfig: Didn't find expected font family. Perhaps URW Type 1 fonts need installing? while printing string Ludwig with font Helvetica gdImageStringFT: fontconfig: Didn't find expected font family. Perhaps URW Type 1 fonts need installing? while printing string Cannon Box with font Helvetica gdImageStringFT: fontconfig: Didn't find expected font family. Perhaps URW Type 1 fonts need installing? while printing string Propeller Box with font Helvetica gdImageStringFT: fontconfig: Didn't find expected font family. Perhaps URW Type 1 fonts need installing? while printing string Goomba Mask with font Helvetica gdImageStringFT: fontconfig: Didn't find expected font family. Perhaps URW Type 1 fonts need installing? while printing string Bullet Bill Mask with font Helvetica gdImageStringFT: fontconfig: Didn't find expected font family. Perhaps URW Type 1 fonts need installing? while printing string Red POW Box with font Helvetica gdImageStringFT: fontconfig: Didn't find expected font family. Perhaps URW Type 1 fonts need installing? while printing string ON/OFF Trampoline with font Helvetica etc... ```

Platform

[ ] cross-platform issue - linux
[x] cross-platform issue - windows
[ ] cross-platform issue - macos

Environment Details:

OS: Windows 10
OS Version: 21H2
Compiler: MinGW64 GCC
Compiler version: 11.2.0

alandefreitas / matplotplusplus

Cannot modify font used to render charts #264