fix: reduce lookups in whoami call

[aeneasr]

Related issue(s)

Checklist

• I have read the contributing guidelines.
• I have referenced an issue containing the design document if my change
  introduces a new feature.
• I am following the
  contributing code guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security vulnerability, I
  confirm that I got the approval (please contact
  security@ory.sh) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further Comments

[codecov]

Codecov Report

Merging #3364 (f4450d6) into master (b1e78ad) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head f4450d6 differs from pull request most recent head 3b593b3. Consider uploading reports for the commit 3b593b3 to get more accurate results

@@           Coverage Diff           @@
##           master    #3364   +/-   ##
=======================================
  Coverage   77.96%   77.97%           
=======================================
  Files         326      326           
  Lines       21214    21214           
=======================================
+ Hits        16540    16542    +2     
+ Misses       3444     3443    -1     
+ Partials     1230     1229    -1     

Impacted Files	Coverage Δ
identity/credentials.go	83.67% <ø> (ø)
session/manager_http.go	78.42% <100.00%> (ø)
session/test/persistence.go	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes