Update testbench.md (fix broken links)

[humble-barnacle001]

Ref #285

Changes done:

• [x] Task 1: Fixed the link to Testbench in docs

Screenshots:

Preview Link(s): https://github.com/humble-barnacle001/CircuitVerseDocs/blob/patch-1/docs/testbench.md

✅️ By submitting this PR, I have verified the following

• [x] Checked to see if a similar PR has already been opened 🤔️
• [x] Reviewed the contributing guidelines 🔍️
• [x] Sample preview link added (add a link from the checks tab after checks complete)
• [x] Tried Squashing the commits into one