skip unnecessary github actions steps

Summary:
X-link: https://github.com/facebookincubator/zstrong/pull/1100

Update generated github actions to only run the fetch and and build steps when there are sources expected for a manifest

For local github actions testing using `act` this speeds up the test runs, and in real github CI it makes it clearer which steps are actually doing something on the given runner (we don't know exactly what it has installed beforehand)

Also set the windows git config the same as on internal CI

Reviewed By: bigfootjon

Differential Revision: D67839708

fbshipit-source-id: 0a60c6fc89e8c6abb2464f879459aa23d5aec969

build/fbcode_builder/getdeps/fetcher.py

@@ -244,7 +244,9 @@ class GitFetcher(Fetcher):
                     if not m:
                         raise Exception("Failed to parse rev from %s" % hash_file)
                     rev = m.group(1)
-                    print("Using pinned rev %s for %s" % (rev, repo_url))
+                    print(
+                        "Using pinned rev %s for %s" % (rev, repo_url), file=sys.stderr
+                    )
 
         self.rev = rev or "main"
         self.origin_repo = repo_url