[meta] Teach fabricate about alpha and beta release

Author: olafmersmann

scripts/fabricate

@@ -150,9 +150,14 @@ def git_version(format="pep440"):
         version, offset, hash = res
         offset = int(offset)
         major, minor, release = version.split(".")
-        if "rc" in release:
-            release = release[:release.index("rc")]
-                    
+        is_prerelease = False
+        for suffix in ["a", "b", "rc"]:
+            if suffix in release:
+                release = release[:release.index(suffix)]
+                is_prerelease = True
+        if is_prerelease:
+            release = int(release) - 1
+
         if format == "pep440":
             return f"{major}.{minor}.{int(release) + 1}-dev{offset}+{hash}"
         elif format == "rust":