Bump golang version and update unit tests to reflect new mtls error string

[KyleWiese]

In newer golang versions (likely from this change), the cli unit tests fail with:

--- FAIL: TestMutualTLSNoCerts (0.01s)
    edge_client_test.go:286: want remote error: tls: bad certificate, got Get "https://127.0.0.1:35291/v1/organizations/org/environments/env": remote error: tls: certificate required 

Updating the unit test to reflect the current error string.

[codecov[bot]]

Codecov Report

Merging #255 (15d7c5c) into main (1b352db) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #255   +/-   ##
=======================================
  Coverage   80.43%   80.43%           
=======================================
  Files          17       17           
  Lines        1748     1748           
=======================================
  Hits         1406     1406           
  Misses        183      183           
  Partials      159      159           

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[theganyo]

@KyleWiese We should probably update the other repos to the same Go version for consistency.