Point to the new pylxd package repo in requirements.txt

[devspyrosv]

The pylxd package seems to have moved to https://github.com/canonical/pylxd.

This PR updates the entry in the file requirements.txt

---

This is the same as PR #82 but from a branch belonging to the repository.

This way the secrets will be accessible in the workflows.

[github-actions]

Test coverage for 92c46b3

Name                                    Stmts   Miss Branch BrPart  Cover   Missing
-----------------------------------------------------------------------------------
src/charm.py                              371     86     86     21    74%   126-128, 182-190, 202-206, 275->279, 300-305, 315, 324-325, 334-345, 362-364, 372-375, 381, 392, 403->420, 408-413, 430-431, 435-436, 441-444, 457-458, 460-461, 495-503, 514-515, 533-535, 538->exit, 542-544, 567-572, 582-583, 585-586, 588-589, 624->626, 685-686, 699, 712
src/errors.py                              22      0      0      0   100%
src/event_timer.py                         42      8      4      0    74%   96-99, 119-122
src/firewall.py                            43     25     10      0    38%   38-42, 64-67, 75-149
src/github_type.py                         36      0      0      0   100%
src/lxd_type.py                            38      0      2      0   100%
src/repo_policy_compliance_service.py       5      5      0      0     0%   4-14
src/runner.py                             245     29     74     21    84%   40->44, 184-191, 197-203, 262-267, 272, 292, 325->328, 331-333, 340, 354, 364, 368, 370, 385, 429-434, 444, 528, 561, 587, 592-604, 618, 636
src/runner_manager.py                     203     24     80      8    87%   196-198, 211-212, 224-226, 232-237, 241-242, 252-253, 306, 331-335, 354, 372, 488, 508
src/runner_type.py                         48      0     10      0   100%
src/utilities.py                           64      4     16      6    88%   74->76, 78->84, 89-91, 157, 210
-----------------------------------------------------------------------------------
TOTAL                                    1117    181    282     56    81%

Static code analysis report

Run started:2023-07-11 17:42:17.547654

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 2495
  Total lines skipped (#nosec): 0
  Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 9

Run metrics:
  Total issues (by severity):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
  Total issues (by confidence):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
Files skipped (0):

[arturo-seijas]

LGTM