dependencies: Add a get_version method to Python3Dependency
dependencies: Add a get_version method to Python3Dependency

Otherwise ninja files regeneration fails with:

  AttributeError: 'Python3Dependency' object has no attribute 'get_version'

mesonbuild/meson,pexip/meson,aaronp24/meson,becm/meson,wberrier/meson,fmuellner/meson,becm/meson,jeandet/meson,QuLogic/meson,mesonbuild/meson,centricular/meson,trhd/meson,jpakkane/meson,pexip/meson,jpakkane/meson,MathieuDuponchelle/meson,thiblahute/meson,mesonbuild/meson,thiblahute/meson,jeandet/meson,centricular/meson,MathieuDuponchelle/meson,wberrier/meson,thiblahute/meson,pexip/meson,aaronp24/meson,mesonbuild/meson,jeandet/meson,trhd/meson,jpakkane/meson,QuLogic/meson,pexip/meson,QuLogic/meson,fmuellner/meson,fmuellner/meson,trhd/meson,centricular/meson,QuLogic/meson,fmuellner/meson,rhd/meson,MathieuDuponchelle/meson,pexip/meson,trhd/meson,thiblahute/meson,rhd/meson,ernestask/meson,wberrier/meson,fmuellner/meson,thiblahute/meson,centricular/meson,rhd/meson,thiblahute/meson,becm/meson,MathieuDuponchelle/meson,pexip/meson,centricular/meson,MathieuDuponchelle/meson,QuLogic/meson,aaronp24/meson,jpakkane/meson,becm/meson,mesonbuild/meson,QuLogic/meson,becm/meson,rhd/meson,fmuellner/meson,thiblahute/meson,pexip/meson,becm/meson,becm/meson,trhd/meson,jeandet/meson,becm/meson,trhd/meson,trhd/meson,trhd/meson,jeandet/meson,ernestask/meson,pexip/meson,jeandet/meson,thiblahute/meson,aaronp24/meson,trhd/meson,mesonbuild/meson,jpakkane/meson,fmuellner/meson,QuLogic/meson,aaronp24/meson,jeandet/meson,MathieuDuponchelle/meson,ernestask/meson,fmuellner/meson,wberrier/meson,centricular/meson,jpakkane/meson,centricular/meson,wberrier/meson,ernestask/meson,pexip/meson,ernestask/meson,MathieuDuponchelle/meson,MathieuDuponchelle/meson,ernestask/meson,QuLogic/meson,jeandet/meson,wberrier/meson,QuLogic/meson,ernestask/meson,rhd/meson,aaronp24/meson,pexip/meson,rhd/meson,MathieuDuponchelle/meson,jeandet/meson,aaronp24/meson,jpakkane/meson,becm/meson,wberrier/meson,jpakkane/meson,rhd/meson,becm/meson,wberrier/meson,ernestask/meson,mesonbuild/meson,jpakkane/meson,thiblahute/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,aaronp24/meson,rhd/meson,ernestask/meson,centricular/meson,fmuellner/meson,aaronp24/meson