remove uses of golang.org/x/sys/execabs

[thaJeztah]

the "golang.org/x/sys/execabs" package was introduced to address a security issue on Windows, and changing the default behavior of os/exec was considered a breaking change. go1.19 applied the behavior that was previously implemented in the execabs package;

from the release notes: https://go.dev/doc/go1.19#os-exec-path

Command and LookPath no longer allow results from a PATH search to be found
relative to the current directory. This removes a common source of security
problems but may also break existing programs that depend on using, say,
exec.Command("prog") to run a binary named prog (or, on Windows, prog.exe)
in the current directory. See the os/exec package documentation for information
about how best to update such programs.

On Windows, Command and LookPath now respect the NoDefaultCurrentDirectoryInExePath
environment variable, making it possible to disable the default implicit search
of “.” in PATH lookups on Windows systems.

With those changes, we no longer need to use the execabs package, and we can switch back to os/exec.

[thaJeztah]

actually; let me change go.mod to go1.19 (as 1.18 doesn't have that fix)

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (da93839) 55.55% compared to head (3d84f97) 55.55%.

❗ Current head 3d84f97 differs from pull request most recent head 37c4a6b. Consider uploading reports for the commit 37c4a6b to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #270   +/-   ##
=======================================
  Coverage   55.55%   55.55%           
=======================================
  Files           9        9           
  Lines         666      666           
=======================================
  Hits          370      370           
  Misses        253      253           
  Partials       43       43           

Impacted Files	Coverage Δ
client/command.go	0.00% <ø> (ø)

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