Fix: Add missing empty spaces in exit / die message for invalid certificate path

[cybersec-jochenarnold]

Add missing empty spaces in error message

Description

Two missing spaces were added to the exit / die message for invalid certificate paths.
Improves readability of error message and included file path.

Which issue(s) this PR fixes:

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)