Add upgrading of linux kernel

[yhaliaw]

Automatically upgrade the kernel to avoid a possible bug in the 5.15 version of the kernel.
This should be a temporary fix as new version of Ubuntu would include newer kernel by default in the future.

[github-actions]

Lint checks failed for 7d5693b

```

src/charm.py:40: error: Module "ops.model" has no attribute "JsonObject" [attr-defined]
Found 1 error in 1 file (checked 23 source files)

[github-actions]

Test coverage for 7d5693b

Name                                    Stmts   Miss Branch BrPart  Cover   Missing
-----------------------------------------------------------------------------------
src/charm.py                              372     86     86     21    74%   129-131, 185-193, 205-209, 278->282, 303-308, 318, 327-328, 337-348, 365-367, 375-378, 384, 395, 406->423, 411-416, 433-434, 438-439, 444-447, 460-461, 463-464, 498-506, 517-518, 536-538, 541->exit, 545-547, 570-575, 585-586, 588-589, 591-592, 627->629, 688-689, 702, 715
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                             228     29     64     21    82%   39->43, 170-177, 183-189, 248-253, 258, 278, 311->314, 317-319, 326, 340, 350, 354, 356, 371, 405-410, 420, 504, 537, 563, 568-580, 594, 612
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                                    1101    181    272     56    81%

Static code analysis report

Run started:2023-07-04 06:18:37.615730

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 2468
  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):

[yanksyoon]

LGTM!