Revert "Unpin the pip version in setupVirtualenv (#36745)"

This reverts commit 0274331.

Author: shunping

.github/trigger_files/beam_PreCommit_Python_ML.json

@@ -1,4 +0,0 @@
-{
-  "comment": "Modify this file in a trivial way to cause this test suite to run.",
-  "modification": 0
-}

buildSrc/src/main/groovy/org/apache/beam/gradle/BeamModulePlugin.groovy

@@ -3122,8 +3122,12 @@ class BeamModulePlugin implements Plugin<Project> {
           }
           project.exec {
             executable 'sh'
+            // TODO: https://github.com/apache/beam/issues/29022
+            // pip 23.3 is failing due to Hash mismatch between expected SHA of the packaged and actual SHA.
+            // until it is resolved on pip's side, don't use pip's cache.
+            // pip 25.1 casues :sdks:python:installGcpTest stuck. Pin to 25.0.1 for now.
             args '-c', ". ${project.ext.envdir}/bin/activate && " +
-                "pip install --pre --retries 10 --upgrade pip --no-cache-dir && " +
+                "pip install --pre --retries 10 --upgrade pip==25.0.1 --no-cache-dir && " +
                 "pip install --pre --retries 10 --upgrade tox --no-cache-dir"
           }
         }