upgrade pip just before building wheel

Author: jswhit

.github/workflows/build-wheels.yml

@@ -117,6 +117,7 @@ jobs:
         echo "------- BEFORE INSTALL --------"
         before_install
         echo "------- CLEAN CODE --------"
+        python -m pip install --upgrade pip
         /bin/rm -rf $REPO_DIR
         git clone https://github.com/Unidata/${REPO_DIR}
         cd $REPO_DIR