Fix invalid .gitignore on *.import files

Those define how the resources must be imported, and can
therefore contain important information (e.g. whether filters
should be used).

3d/material_testers/icon.png.import

@@ -0,0 +1,28 @@
+[remap]
+
+importer="texture"
+type="StreamTexture"
+path="res://.import/icon.png-487276ed1e3a0c39cad0279d744ee560.stex"
+
+[deps]
+
+source_md5="20b8fc864101393c6caf46d0bff09549"
+
+[params]
+
+compress/mode=0
+compress/lossy_quality=0.7
+compress/hdr_mode=0
+compress/normal_map=0
+flags/repeat=0
+flags/filter=true
+flags/mipmaps=false
+flags/anisotropic=false
+flags/srgb=2
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/HDR_as_SRGB=false
+stream=false
+size_limit=0
+detect_3d=true
+svg/scale=1.0