Raise error if markup in MarkupText is invalid

[PhilippImhof]

This is linked to ManimCommunity/ManimPango#8 and ManimCommunity/ManimPango#9.

As soon as the other PR is merged, MarkupText will raise an error when the markup is invalid, e.g. invalid tags or valid unbalanced tags.

from manim import *

class TestValidation(Scene):
    def construct(self):
        text1=MarkupText("bla") 
        text2=MarkupText("<b>bla</b>") 
        text3=MarkupText('<color col="RED">bla</color>')
        text4=MarkupText("<asdf>bla</asdf>")
        text5=MarkupText("<b>bla")

The last two will fail, the others will be OK.

[PhilippImhof]

Setting this to draft as long as ManimPango is not updated, because it will obviously break MarkupText.

No permissions. @naveen521kk could you please.

[naveen521kk]

I have released a v0.1.6. Update to that, by setting that as the minimum using poetry and update.

[naveen521kk]

Also, set the minimum version to v0.1.6 in pyproject.toml