Added *.listing extension to TeX.gitignore

This is the default extension the package "tcolorbox" may generate. The actual extension may be changed by key "listing file" provided by "tcolorbox".

TeX.gitignore

@@ -188,6 +188,9 @@ sympy-plots-for-*.tex/
 *.pytxcode
 pythontex-files-*/
 
+# tcolorbox
+*.listing
+
 # thmtools
 *.loe