Blow up on Jenkins build if engine version is not a tag.

Fixes #3347

Tools/gen_build_info.py

@@ -50,7 +50,7 @@ def generate_manifest(dir: str) -> str:
 
 
 def get_engine_version() -> str:
-    proc = subprocess.run(["git", "describe", "--tags", "--abbrev=0"], stdout=subprocess.PIPE, cwd="RobustToolbox", check=True, encoding="UTF-8")
+    proc = subprocess.run(["git", "describe", "--exact-match", "--tags", "--abbrev=0"], stdout=subprocess.PIPE, cwd="RobustToolbox", check=True, encoding="UTF-8")
     tag = proc.stdout.strip()
     assert tag.startswith("v")
     return tag[1:] # Cut off v prefix.