only ignore sdkconfig* files in the espressif port's top directory

danh and microdev1 noticed that this ignore pattern was over-broad
and caused added sdkconfig files in boards/ (which should be committed)
to be ignored and not proposed for addition by common tools like
git status, git gui, etc.

This pattern anchors the search so that it only matches in the
ports/espressif directory, so ports/espressif/sdkconfig is ignored
but ports/espressif/boards/example/sdkconfig is not ignored anymore

Author: jepler

ports/espressif/.gitignore

@@ -1,5 +1,5 @@
 # idf.py menuconfig
-./sdkconfig*
+/sdkconfig*
 
 # lock files for examples and components
 dependencies.lock