Bump minimum supported version of Pex to v2.1.129. (pantsbuild#18678)

e8d387b made it so the "ambient"
Python interpreter used to run Pex is always the scie-provided interpreter
(currently Python 3.9). This increases the chances that the interpreter used
to run Pex won't match the interpreter constraints configured for user code
in Pants. Until Pex v2.1.129, this mismatch would cause errors when
resolving / building VCS and local project requirements (see
pex-tool/pex#2092). Bump the minimum supported
version of Pex to the first with a fix for that issue, to prevent users pinning
`[pex-cli].version` from silently breaking their setups by upgrading Pants
without also upgrading Pex.

Resolves pantsbuild#18662

src/python/pants/backend/python/util_rules/pex_cli.py

@@ -37,7 +37,7 @@ class PexCli(TemplatedExternalTool):
 
     default_version = "v2.1.131"
     default_url_template = "https://github.com/pantsbuild/pex/releases/download/{version}/pex"
-    version_constraints = ">=2.1.124,<3.0"
+    version_constraints = ">=2.1.129,<3.0"
 
     @classproperty
     def default_known_versions(cls):