I am using MacOS and had same issue where composer was using powershell and not bash. Following settings in the settings.json worked for me -
"terminal.integrated.automationProfile.osx": {},
"terminal.integrated.defaultProfile.osx": "bash",
"terminal.integrated.shellIntegration.enabled": false,
"terminal.integrated.defaultProfile.linux": "bash"
Importantly, it did not work until I set the Linux profile as well to ‘bash’