Python: small makefile update for python (#9847)

### Motivation and Context

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Small fix in the makefile for when uv is not installed.

### Description

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### Contribution Checklist

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- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

python/Makefile

@@ -34,17 +34,20 @@ install:
 	make install-sk
 	make install-pre-commit
 
-UV_VERSION = $(shell uv --version 2> /dev/null)
+UV_VERSION := $(shell command -v uv 2> /dev/null)
 install-uv:
 # Check if uv is installed
-ifdef UV_VERSION
-	echo "uv found $(UV_VERSION)"
-	echo "running uv update"
-	uv self update 
-else
+ifndef UV_VERSION
 	echo "uv could not be found"
 	echo "Installing uv"
 	curl -LsSf https://astral.sh/uv/install.sh | sh
+	echo "uv installed"
+	echo "Please restart your shell."
+	exit 1
+else
+	echo "uv found $(UV_VERSION)"
+	echo "running uv update"
+	uv self update 
 endif
 
 .ONESHELL: