chore: bump which dependency to v4

[mxschmitt]

This internally was throwing this before (ignored via silent catch()):

Error: UNC host 'cpc-maxsc-heqga' access is not allowed
    at stat (C:\Users\maxschmitt\Developer\playwright-vscode\lib\fs.js:1597:10)
    at Object.stat (C:\Users\maxschmitt\Developer\playwright-vscode\lib\electron\js2c\node_init.js:2:4911)
    at isexe (c:\Users\maxschmitt\Developer\playwright-vscode\node_modules\isexe\windows.js:35:6)
    at isexe (c:\Users\maxschmitt\Developer\playwright-vscode\node_modules\isexe\index.js:34:3)
    at c:\Users\maxschmitt\Developer\playwright-vscode\node_modules\isexe\index.js:24:7
    at new Promise (<anonymous>)
    at isexe (c:\Users\maxschmitt\Developer\playwright-vscode\node_modules\isexe\index.js:23:12)
    at which2 (c:\Users\maxschmitt\Developer\playwright-vscode\node_modules\which\lib\index.js:63:24)
    at findNode (c:\Users\maxschmitt\Developer\playwright-vscode\src\utils.ts:153:12)
    at PlaywrightTest._runNode (c:\Users\maxschmitt\Developer\playwright-vscode\src\playwrightTest.ts:279:29)
    at PlaywrightTest._getPlaywrightInfoImpl (c:\Users\maxschmitt\Developer\playwright-vscode\src\playwrightTest.ts:76:21)
    at PlaywrightTest.getPlaywrightInfo (c:\Users\maxschmitt\Developer\playwright-vscode\src\playwrightTest.ts:71:14)
    at Extension._rebuildModel (c:\Users\maxschmitt\Developer\playwright-vscode\src\extension.ts:250:26)
    at Extension.activate (c:\Users\maxschmitt\Developer\playwright-vscode\src\extension.ts:208:5) {code: 'ERR_UNC_HOST_NOT_ALLOWED', stack: 'Error: UNC host 'cpc-maxsc-heqga' access is n…per\playwright-vscode\src\extension.ts:208:5)', message: 'UNC host 'cpc-maxsc-heqga' access is not allowed', toString: ƒ, Symbol(kIsNodeError): true}

Fixes microsoft/playwright#29898