fix: correctly copy binaries in make install

[coadler]

Since it copied to a nested directory, it's very confusing if you
already had a coder binary in your ~/go/bin, since it would always
prefer the coder in the higher directory.

[codecov]

Codecov Report

Merging #517 (3b11f0b) into main (b55a67a) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #517      +/-   ##
==========================================
- Coverage   68.11%   68.10%   -0.02%     
==========================================
  Files         164      161       -3     
  Lines        9309     9129     -180     
  Branches       85       85              
==========================================
- Hits         6341     6217     -124     
+ Misses       2344     2305      -39     
+ Partials      624      607      -17     

Flag	Coverage Δ
unittest-go-macos-latest	62.62% <ø> (+0.06%)	⬆️
unittest-go-ubuntu-latest	67.44% <ø> (-0.22%)	⬇️
unittest-go-windows-2022	?
unittest-js	63.63% <ø> (ø)

Impacted Files	Coverage Δ
provisionersdk/serve.go	35.13% <0.00%> (-8.11%)	⬇️
pty/ptytest/ptytest.go	94.44% <0.00%> (-5.56%)	⬇️
provisionerd/provisionerd.go	77.57% <0.00%> (-1.11%)	⬇️
peer/conn.go	80.56% <0.00%> (-0.77%)	⬇️
coderd/provisionerdaemons.go	57.06% <0.00%> (-0.55%)	⬇️
agent/usershell/usershell_windows.go
pty/start_windows.go
pty/pty_windows.go
provisionersdk/transport.go	85.10% <0.00%> (+6.38%)	⬆️
peerbroker/dial.go	82.45% <0.00%> (+7.01%)	⬆️

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