Compiler warnings preventing musl builds for c0.3.0

[cpswan]

Describe the bug

warning: format string is not a string literal (potentially insecure) [-Wformat-security]

From the c0.3.0 build workflow where the musl builds fail with:

#9 31.84   112 |       fprintf(stdout, usage);
#9 31.84       |                       ^~~~~
#9 31.84 /sshnpd/sshnpd/build/_deps/atsdk-src/packages/atauth/src/atactivate_arg_parser.c:112:23: note: treat the string as an argument to avoid this
#9 31.84   112 |       fprintf(stdout, usage);
#9 31.84       |                       ^
#9 31.84       |                       "%s", 
#9 31.84 /sshnpd/sshnpd/build/_deps/atsdk-src/packages/atauth/src/atactivate_arg_parser.c:116:23: warning: format string is not a string literal (potentially insecure) [-Wformat-security]
#9 31.84   116 |       fprintf(stderr, usage);
#9 31.84       |                       ^~~~~
#9 31.84 /sshnpd/sshnpd/build/_deps/atsdk-src/packages/atauth/src/atactivate_arg_parser.c:116:23: note: treat the string as an argument to avoid this
#9 31.84   116 |       fprintf(stderr, usage);
#9 31.84       |                       ^
#9 31.84       |                       "%s", 
#9 31.84 /sshnpd/sshnpd/build/_deps/atsdk-src/packages/atauth/src/atactivate_arg_parser.c:130:21: warning: format string is not a string literal (potentially insecure) [-Wformat-security]
#9 31.84   130 |     fprintf(stderr, usage);
#9 31.84       |                     ^~~~~
#9 31.84 /sshnpd/sshnpd/build/_deps/atsdk-src/packages/atauth/src/atactivate_arg_parser.c:130:21: note: treat the string as an argument to avoid this
#9 31.84   130 |     fprintf(stderr, usage);
#9 31.84       |                     ^
#9 31.84       |                     "%s", 
#9 31.84 /sshnpd/sshnpd/build/_deps/atsdk-src/packages/atauth/src/atactivate_arg_parser.c:136:21: warning: format string is not a string literal (potentially insecure) [-Wformat-security]
#9 31.84   136 |     fprintf(stderr, usage);
#9 31.84       |                     ^~~~~
#9 31.84 /sshnpd/sshnpd/build/_deps/atsdk-src/packages/atauth/src/atactivate_arg_parser.c:136:21: note: treat the string as an argument to avoid this
#9 31.84   136 |     fprintf(stderr, usage);
#9 31.84       |                     ^
#9 31.84       |                     "%s", 

Steps to reproduce

1. First I bumped versions in chore: Bump version to 0.3.0 and update CHANGELOG #1647
2. Then I created a pre-release for c0.3.0
3. And then the musl builds failed with the warnings above

Expected behavior

Builds with no warnings

[XavierChanth]

fprintf warnings fixed in atsign-foundation/at_c#496
PR fixing another compile warning: atsign-foundation/at_c#506

PR in NoPorts pinned to at_c#506 #1649

[cpswan]

Fixed by #1649