Add internal to .gitignore

DEPS has been added in https://crrev.com/c/4324321, but whtout
.gitignore entry.

R=avi@google.com

Bug: 1409738
Change-Id: I0bd53c417f24281bc21cbabba0e553bc11b8f19f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4584991
Reviewed-by: Avi Drissman <avi@chromium.org>
Auto-Submit: Josip Sokcevic <sokcevic@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1152593}

.gitignore

@@ -245,6 +245,7 @@ vs-chromium-project.txt
 /googleurl
 /gpu/gles2_conform_test
 /infra/.recipe_deps
+/internal
 /ios/third_party/earl_grey/src
 /ios/third_party/earl_grey2/src
 /ios/third_party/edo/src