Fix solarization of dependency graph during CI

         shortened = artifact.name[:-2]
         artifact.rename(testing_dir / shortened)
         subprocess.run(["gunzip", shortened], cwd=testing_dir)
-    with (testing_dir / "deps.svg").open() as fp:
-        deps_svg = fp.read()
-    deps_svg.replace("black", "#586e75").replace("white", "#002b36")
-    with (testing_dir / "deps.svg").open("w") as fp:
-        fp.write(deps_svg)
+    with (testing_dir / "deps.svg").open("r+") as fp:
+        deps_graph = fp.read()
+        fp.seek(0)
+        fp.write(deps_graph.replace("black", "#586e75").replace("white", "#002b36"))
+        fp.truncate()
 
 
 def get_package_releases(project):