Address spelling issues found by CSpell gitlab-ci job.

Problem/Motivation

See https://git.drupalcode.org/project/views_field_view/-/jobs/4006338

$ $CI_PROJECT_DIR/$_WEB_ROOT/core/node_modules/.bin/cspell -c .cspell.json --show-suggestions --show-context --no-progress $_CSPELL_EXTRA $CSPELL_SEARCH || EXIT_CODE=$?
src/Plugin/views/field/View.php:188:56    - Unknown word (forwardslash) -- 'Use a comma (,) or forwardslash (/) separated list of
	 Suggestions: [forwardsearch]
src/Plugin/views/field/View.php:413:32    - Unknown word (behaviour)    -- cause unexpected behaviour, as this will use the
	 Suggestions: [behavior, behaviors, behaver, behaving, belabour]
CSpell: Files checked: 16, Issues found: 2 in 1 file.
$ WORDS_FILE=_cspell_unrecognized_words.txt
$ UPDATED_PROJECT_DICTIONARY=_cspell_updated_project_words.txt
$ touch $_CSPELL_DICTIONARY $WORDS_FILE $UPDATED_PROJECT_DICTIONARY
$ if [ "$EXIT_CODE" != "" ]; then # collapsed multi-line command
CSpell: Files checked: 17, Issues found: 2 in 1 file.
The number of distinct unrecognised/misspelled words is 2
------------
behaviour
forwardslash
------------

Steps to reproduce

See https://git.drupalcode.org/project/views_field_view/-/jobs/4006338

Proposed resolution

- Update text in code to fix spelling issues.
- Update gitlab-ci.yml so that if a merge request introduces new cspell errors, the merge request can not be merged until the errors are addressed.

See: https://www.drupal.org/docs/develop/git/using-gitlab-to-contribute-to-dr...

cspell:
  allow_failure: false

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Remaining tasks

Merge request

User interface changes

N/A

API changes

N/A

Data model changes

N/A