Fixes #2793 - replace use of [[ conditionals (#2794)

## Summary

Fixes #2793 - use of zsh/bash conditionals in a file with a pure sh
shebang.

## How was it tested?

## Community Contribution License

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[Apache 2 License](https://www.apache.org/licenses/LICENSE-2.0).

By creating this pull request, I represent that I have the right to
license the
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---------

Signed-off-by: Tim Gates <tim.gates@iress.com>

Author: timgates42

plugins/python/venvShellHook.sh

@@ -35,17 +35,15 @@ if [ -d "$VENV_DIR" ]; then
             echo "Do you want to overwrite it? (y/n)"
             read reply
             echo
-            if [[ $reply =~ ^[Yy]$ ]]; then
-                echo "Overwriting existing virtual environment..."
-                create_venv
-            elif [[ $reply =~ ^[Nn]$ ]]; then
-                echo "Using your existing virtual environment. We recommend changing \$VENV_DIR to a different location"
-                touch "$STATE_FILE"
-                exit 0
-            else
-                echo "Invalid input. Exiting..."
-                exit 1
-            fi
+            case "$reply" in
+                [Yy]) echo "Overwriting existing virtual environment..."
+                    create_venv ;;
+                [Nn]) echo "Using your existing virtual environment. We recommend changing \$VENV_DIR to a different location"
+                    touch "$STATE_FILE"
+                    exit 0 ;;
+                *) echo "Invalid input. Exiting..."
+                    exit 1 ;;
+            esac
         fi
     else
         echo "Directory exists but is not a valid virtual environment. Creating a new one..."