Run bwrap tests as separate tests

[adombeck]

Instead of running all bwrap tests as subtests of TestUsersLockingInBubbleWrap, we now run them all with the exact test name which they are defined as. This has multiple benefits:

• It makes it easier to selectively run tests via go test -run <pattern>.
• It fixes test caching: Previously, if the tests succeeded once, they wouldn't be run again even if the implementation was changed.
• It avoids using build tags in locking_bwrap_test.go, which allows golangci-lint to check it (our CI didn't catch the linter errors in that file before, because we don't run golangci-lint with the build tag there).

[adombeck]

I pushed another commit which avoids compiling a new test binary (see the commit message).

[codecov-commenter]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 87.78%. Comparing base (1cc962a) to head (d313666). :warning: Report is 15 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1129   +/-   ##
=======================================
  Coverage   87.78%   87.78%           
=======================================
  Files          89       89           
  Lines        6150     6150           
  Branches      111      111           
=======================================
  Hits         5399     5399           
  Misses        695      695           
  Partials       56       56           

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