fix(tests): Increase git buffer size so cfn/sam schemas can be downloaded

Currently the integration tests in #3042 are failing because the SAM schema fails to download with ```stdout maxBuffer length exceeded```

Increase buffer size

Author: jpinkney-aws

src/shared/extensions/git.ts

@@ -369,7 +369,7 @@ export class GitExtension {
 
                         return execFileAsync(api.git.path, ['cat-file', type, hash], {
                             cwd: tmpDir,
-                            maxBuffer: 1024 * 1024 * 5,
+                            maxBuffer: 1024 * 1024 * 6,
                         }).then(({ stdout }) => stdout)
                     },
                 }))