Fix shell-specific test snapshots (#16688)

## Summary

Two tests were failing when run with `SHELL=fish`:
1. `create_venv_current_working_directory` failed because the "activate"
filter didn't apply properly when the venv was in the CWD. This PR fixes
the filter.
2. `tool_install_warn_path` failed because the messages are different
between fish and bash. This PR hardcodes `SHELL=fish`.

## Test Plan

CI

crates/uv/tests/it/common/mod.rs

@@ -773,8 +773,12 @@ impl TestContext {
             "Activate with: source $1/[BIN]/activate".to_string(),
         ));
         filters.push((
-            r"Activate with: source (.*)/bin/activate(?:\.\w+)?".to_string(),
-            "Activate with: source $1/[BIN]/activate".to_string(),
+            r"Activate with: Scripts\\activate".to_string(),
+            "Activate with: source [BIN]/activate".to_string(),
+        ));
+        filters.push((
+            r"Activate with: source (.*/|)bin/activate(?:\.\w+)?".to_string(),
+            "Activate with: source $1[BIN]/activate".to_string(),
         ));
 
         // Filter non-deterministic temporary directory names
@@ -892,6 +896,12 @@ impl TestContext {
         ))
         .unwrap();
 
+        // Ensure the tests aren't sensitive to the running user's shell without forcing
+        // `bash` on Windows
+        if cfg!(not(windows)) {
+            command.env(EnvVars::SHELL, "bash");
+        }
+
         command
             // When running the tests in a venv, ignore that venv, otherwise we'll capture warnings.
             .env_remove(EnvVars::VIRTUAL_ENV)

crates/uv/tests/it/tool_install.rs

@@ -2848,7 +2848,7 @@ fn tool_install_warn_path() {
         .arg("black==24.1.1")
         .env(EnvVars::UV_TOOL_DIR, tool_dir.as_os_str())
         .env(EnvVars::XDG_BIN_HOME, bin_dir.as_os_str())
-        .env_remove(EnvVars::PATH), @r###"
+        .env_remove(EnvVars::PATH), @r#"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -2865,7 +2865,7 @@ fn tool_install_warn_path() {
      + platformdirs==4.2.0
     Installed 2 executables: black, blackd
     warning: `[TEMP_DIR]/bin` is not on your PATH. To use installed tools, run `export PATH="[TEMP_DIR]/bin:$PATH"` or `uv tool update-shell`.
-    "###);
+    "#);
 }
 
 /// Test installing and reinstalling with an invalid receipt.

crates/uv/tests/it/venv.rs

@@ -1714,7 +1714,7 @@ fn create_venv_current_working_directory() {
     ----- stderr -----
     Using CPython 3.12.[X] interpreter at: [PYTHON-3.12]
     Creating virtual environment at: .
-    Activate with: source bin/activate
+    Activate with: source [BIN]/activate
     "
     );