Print only custom env vars in the test log for each test
Print only custom env vars in the test log for each test

We still print the inherited env at the top of the test log because it
is useful when inspecting test results from a CI.

Fixes https://github.com/mesonbuild/meson/issues/3924

thiblahute/meson,thiblahute/meson,QuLogic/meson,jeandet/meson,pexip/meson,jpakkane/meson,thiblahute/meson,QuLogic/meson,pexip/meson,thiblahute/meson,becm/meson,mesonbuild/meson,becm/meson,mesonbuild/meson,jeandet/meson,pexip/meson,pexip/meson,mesonbuild/meson,becm/meson,becm/meson,jeandet/meson,thiblahute/meson,becm/meson,QuLogic/meson,jpakkane/meson,becm/meson,QuLogic/meson,mesonbuild/meson,thiblahute/meson,QuLogic/meson,mesonbuild/meson,MathieuDuponchelle/meson,jeandet/meson,mesonbuild/meson,mesonbuild/meson,jeandet/meson,MathieuDuponchelle/meson,pexip/meson,jeandet/meson,jpakkane/meson,MathieuDuponchelle/meson,MathieuDuponchelle/meson,MathieuDuponchelle/meson,MathieuDuponchelle/meson,MathieuDuponchelle/meson,jpakkane/meson,mesonbuild/meson,QuLogic/meson,thiblahute/meson,mesonbuild/meson,MathieuDuponchelle/meson,becm/meson,jpakkane/meson,pexip/meson,jpakkane/meson,pexip/meson,mesonbuild/meson,pexip/meson,MathieuDuponchelle/meson,jpakkane/meson,becm/meson,QuLogic/meson,QuLogic/meson,jpakkane/meson,becm/meson,pexip/meson,thiblahute/meson,thiblahute/meson,jeandet/meson,becm/meson,QuLogic/meson,pexip/meson,jpakkane/meson,jeandet/meson,jeandet/meson