Changing references of lightning master to main

[runora95]

Context:
The default branch of pennylane-lightning will be changed from master to main. The references to master need to be updated.

Description of the Change:
Change references of master to main

Benefits:
The default branch gets updated.

Possible Drawbacks:
None

Related GitHub Issues:

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.70%. Comparing base (274fd42) to head (29630f5).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1356      +/-   ##
==========================================
- Coverage   95.69%   94.70%   -0.99%     
==========================================
  Files         278      329      +51     
  Lines       40965    47463    +6498     
==========================================
+ Hits        39200    44952    +5752     
- Misses       1765     2511     +746     

Flag	Coverage Δ
unit_tests	94.70% <100.00%> (-0.99%)	⬇️

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[blacksmith-sh]

Found 5 test failures on Blacksmith runners:

Failures

Test	View Logs
coverage: platform linux, python 3.12/12-final-0	View Logs
coverage: platform linux, python 3.12/12-final-0	View Logs
TestQFT/test_preprocess_qft_decomposition[13]	View Logs
TestQFT/test_preprocess_qft_decomposition[13]	View Logs
TestSerializeOps/test_integration[True-wires_map0]	View Logs