PYTHON-2507 Future proof pip version upgrade for test suite (#549)

Author: ShaneHarvey

.evergreen/config.yml

@@ -866,7 +866,6 @@ tasks:
     - name: "release"
       tags: ["release"]
       exec_timeout_secs: 216000  # 60 minutes (manylinux task is slow).
-      git_tag_only: true
       commands:
         - command: shell.exec
           type: test
@@ -2712,6 +2711,7 @@ buildvariants:
   matrix_spec:
     platform: [ubuntu-20.04, windows-64-vsMulti-small, macos-1014]
   display_name: "Release ${platform}"
+  batchtime: 20160 # 14 days
   tasks:
     - name: "release"
 

.evergreen/utils.sh

@@ -25,7 +25,17 @@ createvirtualenv () {
     fi
     # Upgrade to the latest versions of pip setuptools wheel so that
     # pip can always download the latest cryptography+cffi wheels.
-    python -m pip install --upgrade pip setuptools wheel
+    PYTHON_VERSION=$(python -c 'import sys;print("%s.%s" % sys.version_info[:2])')
+    if [[ $PYTHON_VERSION == "3.4" ]]; then
+        # pip 19.2 dropped support for Python 3.4.
+        python -m pip install --upgrade 'pip<19.2'
+    elif [[ $PYTHON_VERSION == "2.7" || $PYTHON_VERSION == "3.5" ]]; then
+        # pip 21 will drop support for Python 2.7 and 3.5.
+        python -m pip install --upgrade 'pip<21'
+    else
+        python -m pip install --upgrade pip
+    fi
+    python -m pip install --upgrade setuptools wheel
 }
 
 # Usage: