don't invoke callback on empty changes

[thomasheyenbrock]

Fixes #2548

This prevents us from firing change handlers on "empty" changes, in particular when calling codeMirror.signal(editorInstance, "change", editorInstance) (we do this when updating metadata stored on the editor objects like variable types, document AST, etc)

[changeset-bot]

🦋 Changeset detected

Latest commit: 5f26b2f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@graphiql/react	Patch
graphiql	Patch

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[github-actions]

The latest changes of this PR are available as canary in npm (based on the declared changesets):

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@graphiql/[email protected]

[codecov]

Codecov Report

Merging #2565 (5f26b2f) into main (2d91916) will increase coverage by 3.75%.
The diff coverage is 24.16%.

@@            Coverage Diff             @@
##             main    #2565      +/-   ##
==========================================
+ Coverage   65.70%   69.46%   +3.75%     
==========================================
  Files          85       71      -14     
  Lines        5106     4156     -950     
  Branches     1631     1376     -255     
==========================================
- Hits         3355     2887     -468     
+ Misses       1747     1264     -483     
- Partials        4        5       +1     

Impacted Files	Coverage Δ
packages/codemirror-graphql/src/lint.ts	100.00% <ø> (ø)
packages/codemirror-graphql/src/results/mode.ts	47.05% <ø> (ø)
packages/codemirror-graphql/src/utils/hintList.ts	95.65% <ø> (ø)
...ckages/codemirror-graphql/src/utils/mode-indent.ts	0.00% <0.00%> (ø)
packages/codemirror-graphql/src/variables/mode.ts	79.48% <ø> (ø)
packages/graphiql-react/src/editor/whitespace.ts	100.00% <ø> (ø)
packages/graphiql-react/src/utility/debounce.ts	0.00% <0.00%> (ø)
packages/graphiql-react/src/editor/tabs.ts	5.76% <5.76%> (ø)
packages/codemirror-graphql/src/variables/lint.ts	46.98% <66.66%> (ø)
packages/codemirror-graphql/src/hint.ts	94.73% <100.00%> (ø)
... and 97 more

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