fix: serialization tags which are not a string

[bednar]

Closes #80

Proposed Changes

Correct serialisation to LineProtocol for tags which are not a string.

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• make test completes successfully
• Commit messages are in semantic format
• Sign CLA (if not already signed)

[codecov-commenter]

Codecov Report

Merging #81 (3bcb197) into master (ae469fd) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master      #81   +/-   ##
=========================================
  Coverage     82.78%   82.78%           
  Complexity      375      375           
=========================================
  Files            23       23           
  Lines           889      889           
=========================================
  Hits            736      736           
  Misses          153      153           

Impacted Files	Coverage Δ
src/InfluxDB2/Point.php	100.00% <100.00%> (ø)

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