editorconfig: add Makefiles to "text files"

The Makefile and makefile fragments use the same indent style than the
rest of the code (with some inconsistencies).

Add them to the relevant .editorconfig section to make life easier for
editors and reviewers.

Signed-off-by: Max Gautier <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: VannTen

.editorconfig

@@ -4,7 +4,7 @@ insert_final_newline = true
 
 # The settings for C (*.c and *.h) files are mirrored in .clang-format.  Keep
 # them in sync.
-[*.{c,h,sh,perl,pl,pm,txt}]
+[{*.{c,h,sh,perl,pl,pm,txt},config.mak.*,Makefile}]
 indent_style = tab
 tab_width = 8