CI: Use latest version of magic

Commits to open_pdks often require recently added features in magic.

.github/Dockerfile

diff --git a/.github/Dockerfile b/.github/Dockerfile
index 031aa7c..84f612d 100644
--- a/.github/Dockerfile
+++ b/.github/Dockerfile
@@ -25,9 +25,9 @@
 RUN yum install -y git tcl tk libjpeg libgomp libXext libSM libXft libffi cairo gettext Xvfb
 RUN yum install -y python3 python3-pip python3-tkinter python3-devel
 
-RUN git clone git://opencircuitdesign.com/magic magic_15102020
+RUN git clone git://opencircuitdesign.com/magic
 
-WORKDIR magic_15102020
+WORKDIR magic
 
 # build
 RUN ./configure --prefix=/build && \