Fixed hardcoded binary path in test

[ranger-ross]

I noticed nightly CI failed in #2789 due to the Cargo build-dir layout changes on nightly.

This PR fixes the failing test by replacing fn find_sccache_binary with CARGO_BIN_EXE_sccache.
To do this I needed to move the test from a unit test to an integration test so that Cargo would set the CARGO_BIN_EXE_* env var

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 74.32%. Comparing base (c037e11) to head (fd8332b).

Files with missing lines	Patch %	Lines
tests/server.rs	94.44%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2790      +/-   ##
==========================================
- Coverage   74.32%   74.32%   -0.01%     
==========================================
  Files          71       72       +1     
  Lines       40789    40772      -17     
==========================================
- Hits        30318    30304      -14     
+ Misses      10471    10468       -3     

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