Fix cat error message on alpine

[ryan-gang]

This pull request includes several changes to improve the handling of error messages and test cases for bash redirection. The most important changes involve updating test cases to handle different error message formats and adding new test stages for redirection.

Updates to test cases:

• internal/stage_r1.go: Added fallback patterns to handle different error message formats for the testR1 function.
• internal/stage_r2.go: Added fallback patterns to handle different error message formats for the testR2 function.
• internal/stage_r4.go: Updated the testR4 function to include additional regex patterns for error message formats.

New test stages for redirection:

• Makefile: Renamed test_vt to test_redirection_w_bash and added new test stages for redirecting stdout and stderr, as well as appending stdout and stderr.

Additionally, a new import was added:

• internal/stage_r1.go: Added the regexp package to handle regular expressions.