Fix pip_compile::missing_venv test (#4224)

A merge kerfuffle from #4222  and #4218 

Now we fail because we genuinely can't find any interpreters since tests
contexts are isolated by default. I'll improve the error message and
maybe add another test case once `main` is fixed.

crates/uv/tests/pip_compile.rs

@@ -131,15 +131,13 @@ fn missing_venv() -> Result<()> {
 
     uv_snapshot!(context.filters(), context.compile()
             .arg("requirements.in"), @r###"
-    success: true
-    exit_code: 0
+    success: false
+    exit_code: 2
     ----- stdout -----
-    # This file was autogenerated by uv via the following command:
-    #    uv pip compile --cache-dir [CACHE_DIR] --exclude-newer 2024-03-25T00:00:00Z requirements.in
 
     ----- stderr -----
     warning: Requirements file requirements.in does not contain any dependencies
-    Resolved 0 packages in [TIME]
+    error: No Python interpreters found in provided path, active virtual environment, or search path
     "###
     );