Use different output filenames in tests pdftitle.cxx and pdfurl.cxx

[ellert]

This Pull request:

Changes or fixes:

This avoids failures when one test overwrites the other's output:

[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from TPad
[ RUN      ] TPad.PDFUrl
ROOT::TestSupport::ForbidDiagnostics::handler(): Diagnostic in 'TCanvas::Print':
pdf file output.pdf has been created
ROOT::TestSupport::ForbidDiagnostics::handler(): Diagnostic in 'TCanvas::Print':
Current canvas added to pdf file output.pdf
ROOT::TestSupport::ForbidDiagnostics::handler(): Diagnostic in 'TCanvas::Print':
Current canvas added to pdf file output.pdf
ROOT::TestSupport::ForbidDiagnostics::handler(): Diagnostic in 'TCanvas::Print':
pdf file output.pdf has been closed
/builddir/build/BUILD/root-6.40.02/graf2d/gpad/test/pdfurl.cxx:33: Failure
Expected equality of these values:
  statCode
    Which is: 1
  0
PDF file was not created.
[  FAILED  ] TPad.PDFUrl (373 ms)
[----------] 1 test from TPad (373 ms total)
[----------] Global test environment tear-down
[==========] 1 test from 1 test suite ran. (374 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] TPad.PDFUrl
 1 FAILED TEST

Checklist:

• tested changes locally
• updated the docs (if necessary)

[github-actions]

Test Results

    23 files      23 suites   3d 12h 56m 16s ⏱️
 3 876 tests  3 871 ✅ 0 💤 5 ❌
78 826 runs  78 821 ✅ 0 💤 5 ❌

For more details on these failures, see this check.

Results for commit 28cff2a.

[guitargeek]

/backport to 6.40

[root-project-bot]

Preparing to backport PR #22722 to branch 6.40 requested by guitargeek

[root-project-bot]

This PR has been backported to branch 6.40: #22729