fix(tests): Remove executable bit from oauth.rs

[cryptomilk]

This fixes distribution tooling incorrectly detecting the rust file starting with a shebang:

*** ERROR: ./usr/share/cargo/registry/sccache-0.10.0/tests/oauth.rs has
shebang which doesn't start with '/' ([deny(rust_2018_idioms)])

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.61%. Comparing base (9fb3841) to head (7ed82ab).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2375      +/-   ##
==========================================
+ Coverage   67.60%   67.61%   +0.01%     
==========================================
  Files          65       65              
  Lines       35471    35471              
==========================================
+ Hits        23979    23983       +4     
+ Misses      11492    11488       -4     

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