test_layer: changed material for unit tests for add_potting_region when connected to Sherlock

[ansjmoody]

Checklist:

• Run unit tests and make sure they all pass
• Check and fix style errors
  - pre-commit command line check
  - Problems tab in PyCharm
• [na] Bench test new/modified APIs by using and modifying the code in the example for the API method
• Add new methods to rst file for updated API script(\doc\source\api)
• Generate documentation
• Verify the HTML. It gets generated at: \doc\build\html.
  - Open index.html
  - Click on "API Reference" at the top.
  - Verify HTML for API changes.
• Check that test code coverage is at least 80% when Sherlock is running and can be connected to using gRPC

[codecov]

Codecov Report

Merging #153 (ea42777) into main (71c1601) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##             main     #153   +/-   ##
=======================================
  Coverage   56.20%   56.20%           
=======================================
  Files          20       20           
  Lines        3112     3112           
=======================================
  Hits         1749     1749           
  Misses       1363     1363           

Files Changed	Coverage Δ
src/ansys/sherlock/core/analysis.py	39.19% <ø> (ø)
src/ansys/sherlock/core/launcher.py	42.66% <0.00%> (ø)