update Pex to 2.77.1

Changelogs:
 * https://github.com/pex-tool/pex/releases/tag/v2.74.0
 * https://github.com/pex-tool/pex/releases/tag/v2.74.1
 * https://github.com/pex-tool/pex/releases/tag/v2.74.2
 * https://github.com/pex-tool/pex/releases/tag/v2.74.3
 * https://github.com/pex-tool/pex/releases/tag/v2.75.0
 * https://github.com/pex-tool/pex/releases/tag/v2.75.1
 * https://github.com/pex-tool/pex/releases/tag/v2.75.2
 * https://github.com/pex-tool/pex/releases/tag/v2.76.0
 * https://github.com/pex-tool/pex/releases/tag/v2.76.1
 * https://github.com/pex-tool/pex/releases/tag/v2.77.0
 * https://github.com/pex-tool/pex/releases/tag/v2.77.1

NOTE: First update since pantsbuild#22979

Author: cburroughs

docs/notes/2.31.x.md

@@ -49,7 +49,7 @@ used by Pants itself works.
 
 Added the `[python].default_to_resolve_interpreter_constraints` option which when set the true, allows Python targets with both `interpreter_constraints` and `resolve` fields to fallback on their resolve's interpreter constraints before the global constraints if no interpreter constraints are set on the actual target.
 
-The version of [Pex](https://github.com/pex-tool/pex) used by the Python backend has been upgraded to [`v2.73.1`](https://github.com/pex-tool/pex/releases/tag/v2.73.1). This fixes two issues:
+The version of [Pex](https://github.com/pex-tool/pex) used by the Python backend has been upgraded to [`v2.77.1`](https://github.com/pex-tool/pex/releases/tag/v2.77.1). This fixes two issues of particular note for Pants users:
 - A [bug](https://github.com/pantsbuild/pants/issues/22886) that hindered the use of multiple custom package indexes
 - A [bug](https://github.com/pex-tool/pex/issues/3032) that prevented invalidation of a lockfile when the URL of a URL-based requirement changed.
 

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

@@ -37,9 +37,9 @@
 logger = logging.getLogger(__name__)
 
 
-_PEX_VERSION = "v2.73.1"
-_PEX_BINARY_HASH = "e6907e079a3f7c917dc88b41d892f732d4b8dbe388abfefc064d19c4a9f3c7e8"
-_PEX_BINARY_SIZE = 4939987
+_PEX_VERSION = "v2.77.1"
+_PEX_BINARY_HASH = "7d80c62ba2119be318518298c0810c2b862a61fd7ce8ba29c811e5e72239569d"
+_PEX_BINARY_SIZE = 4944053
 
 
 class PexCli(TemplatedExternalTool):