ci(digest): Add digest pinning

[merkata]

Applicable spec:

Overview

Adds digest pinning to rockfiles.

Rationale

Adds digest pinning to rockfiles.

Juju Events Changes

n/a

Module Changes

n/a

Library Changes

n/a

Checklist

• [ x] The charm style guide was applied
• [ x] The contributing guide was applied
• [ x] The changes are compliant with ISD054 - Managing Charm Complexity
• [ x] The documentation is generated using src-docs
• [ x] The documentation for charmhub is updated.
• [ x] The PR is tagged with appropriate label (urgent, trivial, complex)

[github-actions]

Test coverage for 0783aeb

Name                Stmts   Miss Branch BrPart  Cover   Missing
---------------------------------------------------------------
src/charm.py          521     37    168     29    90%   197-200, 551, 582, 628, 663-664, 715-722, 727, 829->834, 833, 835, 840-841, 901, 919, 926, 1018, 1027, 1039, 1060, 1069, 1088, 1092, 1121, 1174, 1306, 1328, 1335->1337, 1380->exit, 1392, 1424, 1433-1434
src/cos.py             15      0      0      0   100%
src/exceptions.py      17      1      2      1    89%   41
src/types_.py          15      0      0      0   100%
---------------------------------------------------------------
TOTAL                 568     38    170     30    90%

Static code analysis report

Run started:2023-10-18 21:45:17.965783

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 4250
  Total lines skipped (#nosec): 1
  Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 0

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):