TECH_DEBT: Fail get_deployed_commit.py when the full hash cannot be resolved

The script warned about an unresolved short hash and then published it anyway. The
downstream consumer cannot use it: list-deploy-changes.py fetches both refs with
'git fetch --depth=1 origin <ref>', GitHub rejects unadvertised objects by short SHA,
and that fetch discards stderr and ignores its exit code — so the deployment summary
came out empty with nothing in the log to explain it.

- Replace the short-hash warning with a fail(), reporting the same context on stderr
  and exiting nonzero
- Place it ahead of the FromCommit print and the ##vso[task.setvariable] line, so no
  unusable value is published

This makes the Summarize job fail whenever the GitHub lookup fails for any reason,
including a rate limit or transport error, and Deploy is gated on Summarize
succeeding.

Verified against qa2 that the normal path is unchanged and exits 0. Forced the
failure path with an unreachable API host: the warning and the ERROR line are both
printed, the exit status is 1, and neither FromCommit nor the ##vso line is emitted.

Author: MikeAtPinnacle

Scripts/get_deployed_commit.py

@@ -123,12 +123,13 @@ def main():
         except Exception as e:
             print(f"Warning: Could not resolve full commit hash: {e}", file=sys.stderr)
 
-    # A short hash here breaks the downstream fetch in list-deploy-changes.py, which fails
-    # silently and yields an empty summary. Say so rather than letting it pass unnoticed.
+    # A short hash breaks the downstream fetch in list-deploy-changes.py: 'git fetch origin
+    # <ref>' is rejected for anything but a full SHA, and that failure is swallowed, so the
+    # summary comes out empty with nothing in the log to explain it. Stop here instead of
+    # publishing a FromCommit that cannot be used.
     if len(commit) < 40:
-        print(f"Warning: '{commit}' is not a full commit hash. "
-              f"'git fetch origin {commit}' will fail and the deployment summary may be empty.",
-              file=sys.stderr)
+        fail(f"'{commit}' is not a full commit hash and could not be resolved to one. "
+             f"'git fetch origin {commit}' would fail and the deployment summary would be empty.")
 
     print(f"FromCommit: {commit}")