[NFC] docs/oidc: mark code blocks as JSON, minor syntax fixes

[woodruffw]

No functional changes. Just noticed that these code blocks were missing syntax highlighting while reading the docs.

Signed-off-by: William Woodruff william@trailofbits.com

[woodruffw]

Oh, Codecov...

Run codecov/codecov-action@81cd2dc8148241f03f5839d295e000b8f761e378
==> linux OS detected
Error: certificate has expired
    at TLSSocket.onConnectSecure (node:_tls_wrap:1[5](https://github.com/sigstore/fulcio/runs/7435468531?check_suite_focus=true#step:8:6)30:34)
    at TLSSocket.emit (node:events:390:28)
    at TLSSocket._finishInit (node:_tls_wrap:944:8)
    at TLSWrap.ssl.onhandshakedone (node:_tls_wrap:[7](https://github.com/sigstore/fulcio/runs/7435468531?check_suite_focus=true#step:8:8)25:12)

[haydentherapper]

Thanks! LGTM, just need to wait until codecov fixes its expired cert.

[codecov-commenter]

Codecov Report

Merging #697 (bcc9cc5) into main (91ddddd) will decrease coverage by 0.13%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #697      +/-   ##
==========================================
- Coverage   54.57%   54.44%   -0.14%     
==========================================
  Files          36       36              
  Lines        2228     2228              
==========================================
- Hits         1216     1213       -3     
- Misses        921      923       +2     
- Partials       91       92       +1     

Impacted Files	Coverage Δ
pkg/ca/fileca/load.go	58.62% <0.00%> (-10.35%)	⬇️